On Wed, Sep 11, 2013 at 4:22 PM, Joe Perches <joe@xxxxxxxxxxx> wrote:
> Using vsnprintf or its derivatives with %n can have security
> vulnerability implications.
>
> Prior to commit fef20d9c1380
> ("vsprintf: unify the format decoding layer for its 3 users"),
> any use of %n was ignored.
>
> Reintroduce this feature and convert the existing uses of %n
> to use the return length from vsnprintf or its derivatives.
>
> Signed-off-by: Joe Perches <joe@xxxxxxxxxxx>
> Acked-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx> (proc bits)
> cc: Kees Cook <keescook@xxxxxxxxxxxx>
> cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Yes, please. It might also be worth updating
Documentation/printk-formats.txt to mention that %n has intentionally
removed and will be ignored.
Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>
-Kees
>
> ---
>
> Not particularly well tested...
>
> fs/proc/consoles.c | 2 +-
> fs/proc/nommu.c | 20 ++++++-------
> fs/proc/task_mmu.c | 18 +++++------
> fs/proc/task_nommu.c | 20 ++++++-------
> lib/vsprintf.c | 21 ++++++-------
> net/ipv4/fib_trie.c | 30 ++++++++-----------
> net/ipv4/ping.c | 19 ++++++------
> net/ipv4/tcp_ipv4.c | 84 +++++++++++++++++++++++++---------------------------
> net/ipv4/udp.c | 19 ++++++------
> net/phonet/socket.c | 32 ++++++++++----------
> net/sctp/objcnt.c | 5 ++--
> 11 files changed, 132 insertions(+), 138 deletions(-)
>
> diff --git a/fs/proc/consoles.c b/fs/proc/consoles.c
> index b701eaa..42f2bb7 100644
> --- a/fs/proc/consoles.c
> +++ b/fs/proc/consoles.c
> @@ -47,7 +47,7 @@ static int show_console_dev(struct seq_file *m, void *v)
> con_flags[a].name : ' ';
> flags[a] = 0;
>
> - seq_printf(m, "%s%d%n", con->name, con->index, &len);
> + len = seq_printf(m, "%s%d", con->name, con->index);
> len = 21 - len;
> if (len < 1)
> len = 1;
> diff --git a/fs/proc/nommu.c b/fs/proc/nommu.c
> index ccfd99b..91cfd19 100644
> --- a/fs/proc/nommu.c
> +++ b/fs/proc/nommu.c
> @@ -50,16 +50,16 @@ static int nommu_region_show(struct seq_file *m, struct vm_region *region)
> ino = inode->i_ino;
> }
>
> - seq_printf(m,
> - "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
> - region->vm_start,
> - region->vm_end,
> - flags & VM_READ ? 'r' : '-',
> - flags & VM_WRITE ? 'w' : '-',
> - flags & VM_EXEC ? 'x' : '-',
> - flags & VM_MAYSHARE ? flags & VM_SHARED ? 'S' : 's' : 'p',
> - ((loff_t)region->vm_pgoff) << PAGE_SHIFT,
> - MAJOR(dev), MINOR(dev), ino, &len);
> + len = seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu ",
> + region->vm_start,
> + region->vm_end,
> + flags & VM_READ ? 'r' : '-',
> + flags & VM_WRITE ? 'w' : '-',
> + flags & VM_EXEC ? 'x' : '-',
> + flags & VM_MAYSHARE ?
> + flags & VM_SHARED ? 'S' : 's' : 'p',
> + ((loff_t)region->vm_pgoff) << PAGE_SHIFT,
> + MAJOR(dev), MINOR(dev), ino);
>
> if (file) {
> len = 25 + sizeof(void *) * 6 - len;
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 107d026..f84ee9f 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -286,15 +286,15 @@ show_map_vma(struct seq_file *m, struct vm_area_struct *vma, int is_pid)
> if (stack_guard_page_end(vma, end))
> end -= PAGE_SIZE;
>
> - seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
> - start,
> - end,
> - flags & VM_READ ? 'r' : '-',
> - flags & VM_WRITE ? 'w' : '-',
> - flags & VM_EXEC ? 'x' : '-',
> - flags & VM_MAYSHARE ? 's' : 'p',
> - pgoff,
> - MAJOR(dev), MINOR(dev), ino, &len);
> + len = seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu ",
> + start,
> + end,
> + flags & VM_READ ? 'r' : '-',
> + flags & VM_WRITE ? 'w' : '-',
> + flags & VM_EXEC ? 'x' : '-',
> + flags & VM_MAYSHARE ? 's' : 'p',
> + pgoff,
> + MAJOR(dev), MINOR(dev), ino);
>
> /*
> * Print the dentry name for named mappings, and a
> diff --git a/fs/proc/task_nommu.c b/fs/proc/task_nommu.c
> index 56123a6..1d7bbe5 100644
> --- a/fs/proc/task_nommu.c
> +++ b/fs/proc/task_nommu.c
> @@ -155,16 +155,16 @@ static int nommu_vma_show(struct seq_file *m, struct vm_area_struct *vma,
> pgoff = (loff_t)vma->vm_pgoff << PAGE_SHIFT;
> }
>
> - seq_printf(m,
> - "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu %n",
> - vma->vm_start,
> - vma->vm_end,
> - flags & VM_READ ? 'r' : '-',
> - flags & VM_WRITE ? 'w' : '-',
> - flags & VM_EXEC ? 'x' : '-',
> - flags & VM_MAYSHARE ? flags & VM_SHARED ? 'S' : 's' : 'p',
> - pgoff,
> - MAJOR(dev), MINOR(dev), ino, &len);
> + len = seq_printf(m, "%08lx-%08lx %c%c%c%c %08llx %02x:%02x %lu ",
> + vma->vm_start,
> + vma->vm_end,
> + flags & VM_READ ? 'r' : '-',
> + flags & VM_WRITE ? 'w' : '-',
> + flags & VM_EXEC ? 'x' : '-',
> + flags & VM_MAYSHARE ?
> + flags & VM_SHARED ? 'S' : 's' : 'p',
> + pgoff,
> + MAJOR(dev), MINOR(dev), ino);
>
> if (file) {
> pad_len_spaces(m, len);
> diff --git a/lib/vsprintf.c b/lib/vsprintf.c
> index 26559bd..43c2ea0 100644
> --- a/lib/vsprintf.c
> +++ b/lib/vsprintf.c
> @@ -1683,18 +1683,19 @@ int vsnprintf(char *buf, size_t size, const char *fmt, va_list args)
> break;
>
> case FORMAT_TYPE_NRCHARS: {
> + /* skip %n 's argument */
> u8 qualifier = spec.qualifier;
> + void *skip_arg;
>
> - if (qualifier == 'l') {
> - long *ip = va_arg(args, long *);
> - *ip = (str - buf);
> - } else if (_tolower(qualifier) == 'z') {
> - size_t *ip = va_arg(args, size_t *);
> - *ip = (str - buf);
> - } else {
> - int *ip = va_arg(args, int *);
> - *ip = (str - buf);
> - }
> + WARN_ONCE(1, "Please remove ignored use of %%n in '%s'\n",
> + old_fmt);
> +
> + if (qualifier == 'l')
> + skip_arg = va_arg(args, long *);
> + else if (_tolower(qualifier) == 'z')
> + skip_arg = va_arg(args, size_t *);
> + else
> + skip_arg = va_arg(args, int *);
> break;
> }
>
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index 3df6d3e..ddf1e9c 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -2537,24 +2537,20 @@ static int fib_route_seq_show(struct seq_file *seq, void *v)
> continue;
>
> if (fi)
> - seq_printf(seq,
> - "%s\t%08X\t%08X\t%04X\t%d\t%u\t"
> - "%d\t%08X\t%d\t%u\t%u%n",
> - fi->fib_dev ? fi->fib_dev->name : "*",
> - prefix,
> - fi->fib_nh->nh_gw, flags, 0, 0,
> - fi->fib_priority,
> - mask,
> - (fi->fib_advmss ?
> - fi->fib_advmss + 40 : 0),
> - fi->fib_window,
> - fi->fib_rtt >> 3, &len);
> + len = seq_printf(seq, "%s\t%08X\t%08X\t%04X\t%d\t%u\t%d\t%08X\t%d\t%u\t%u",
> + (fi->fib_dev ?
> + fi->fib_dev->name : "*"),
> + prefix,
> + fi->fib_nh->nh_gw, flags,
> + 0, 0, fi->fib_priority, mask,
> + (fi->fib_advmss ?
> + fi->fib_advmss + 40 : 0),
> + fi->fib_window,
> + fi->fib_rtt >> 3);
> else
> - seq_printf(seq,
> - "*\t%08X\t%08X\t%04X\t%d\t%u\t"
> - "%d\t%08X\t%d\t%u\t%u%n",
> - prefix, 0, flags, 0, 0, 0,
> - mask, 0, 0, 0, &len);
> + len = seq_printf(seq, "*\t%08X\t%08X\t%04X\t%d\t%u\t%d\t%08X\t%d\t%u\t%u",
> + prefix, 0, flags, 0, 0, 0,
> + mask, 0, 0, 0);
>
> seq_printf(seq, "%*s\n", 127 - len, "");
> }
> diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
> index d7d9882..ac8d79f 100644
> --- a/net/ipv4/ping.c
> +++ b/net/ipv4/ping.c
> @@ -1081,16 +1081,15 @@ static void ping_v4_format_sock(struct sock *sp, struct seq_file *f,
> __u16 destp = ntohs(inet->inet_dport);
> __u16 srcp = ntohs(inet->inet_sport);
>
> - seq_printf(f, "%5d: %08X:%04X %08X:%04X"
> - " %02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %d%n",
> - bucket, src, srcp, dest, destp, sp->sk_state,
> - sk_wmem_alloc_get(sp),
> - sk_rmem_alloc_get(sp),
> - 0, 0L, 0,
> - from_kuid_munged(seq_user_ns(f), sock_i_uid(sp)),
> - 0, sock_i_ino(sp),
> - atomic_read(&sp->sk_refcnt), sp,
> - atomic_read(&sp->sk_drops), len);
> + *len = seq_printf(f, "%5d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %d",
> + bucket, src, srcp, dest, destp, sp->sk_state,
> + sk_wmem_alloc_get(sp),
> + sk_rmem_alloc_get(sp),
> + 0, 0L, 0,
> + from_kuid_munged(seq_user_ns(f), sock_i_uid(sp)),
> + 0, sock_i_ino(sp),
> + atomic_read(&sp->sk_refcnt), sp,
> + atomic_read(&sp->sk_drops));
> }
>
> static int ping_v4_seq_show(struct seq_file *seq, void *v)
> diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
> index b14266b..1279c16 100644
> --- a/net/ipv4/tcp_ipv4.c
> +++ b/net/ipv4/tcp_ipv4.c
> @@ -2603,24 +2603,24 @@ static void get_openreq4(const struct sock *sk, const struct request_sock *req,
> const struct inet_request_sock *ireq = inet_rsk(req);
> long delta = req->expires - jiffies;
>
> - seq_printf(f, "%4d: %08X:%04X %08X:%04X"
> - " %02X %08X:%08X %02X:%08lX %08X %5u %8d %u %d %pK%n",
> - i,
> - ireq->loc_addr,
> - ntohs(inet_sk(sk)->inet_sport),
> - ireq->rmt_addr,
> - ntohs(ireq->rmt_port),
> - TCP_SYN_RECV,
> - 0, 0, /* could print option size, but that is af dependent. */
> - 1, /* timers active (only the expire timer) */
> - jiffies_delta_to_clock_t(delta),
> - req->num_timeout,
> - from_kuid_munged(seq_user_ns(f), uid),
> - 0, /* non standard timer */
> - 0, /* open_requests have no inode */
> - atomic_read(&sk->sk_refcnt),
> - req,
> - len);
> + *len = seq_printf(f, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX %08X %5u %8d %u %d %pK",
> + i,
> + ireq->loc_addr,
> + ntohs(inet_sk(sk)->inet_sport),
> + ireq->rmt_addr,
> + ntohs(ireq->rmt_port),
> + TCP_SYN_RECV,
> + 0, 0, /* could print option size,
> + * but that is af dependent.
> + */
> + 1, /* timers active (only the expire timer) */
> + jiffies_delta_to_clock_t(delta),
> + req->num_timeout,
> + from_kuid_munged(seq_user_ns(f), uid),
> + 0, /* non standard timer */
> + 0, /* open_requests have no inode */
> + atomic_read(&sk->sk_refcnt),
> + req);
> }
>
> static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i, int *len)
> @@ -2661,26 +2661,25 @@ static void get_tcp4_sock(struct sock *sk, struct seq_file *f, int i, int *len)
> */
> rx_queue = max_t(int, tp->rcv_nxt - tp->copied_seq, 0);
>
> - seq_printf(f, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX "
> - "%08X %5u %8d %lu %d %pK %lu %lu %u %u %d%n",
> - i, src, srcp, dest, destp, sk->sk_state,
> - tp->write_seq - tp->snd_una,
> - rx_queue,
> - timer_active,
> - jiffies_delta_to_clock_t(timer_expires - jiffies),
> - icsk->icsk_retransmits,
> - from_kuid_munged(seq_user_ns(f), sock_i_uid(sk)),
> - icsk->icsk_probes_out,
> - sock_i_ino(sk),
> - atomic_read(&sk->sk_refcnt), sk,
> - jiffies_to_clock_t(icsk->icsk_rto),
> - jiffies_to_clock_t(icsk->icsk_ack.ato),
> - (icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
> - tp->snd_cwnd,
> - sk->sk_state == TCP_LISTEN ?
> - (fastopenq ? fastopenq->max_qlen : 0) :
> - (tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh),
> - len);
> + *len = seq_printf(f, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %lu %lu %u %u %d",
> + i, src, srcp, dest, destp, sk->sk_state,
> + tp->write_seq - tp->snd_una,
> + rx_queue,
> + timer_active,
> + jiffies_delta_to_clock_t(timer_expires - jiffies),
> + icsk->icsk_retransmits,
> + from_kuid_munged(seq_user_ns(f), sock_i_uid(sk)),
> + icsk->icsk_probes_out,
> + sock_i_ino(sk),
> + atomic_read(&sk->sk_refcnt), sk,
> + jiffies_to_clock_t(icsk->icsk_rto),
> + jiffies_to_clock_t(icsk->icsk_ack.ato),
> + (icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,
> + tp->snd_cwnd,
> + sk->sk_state == TCP_LISTEN ?
> + (fastopenq ? fastopenq->max_qlen : 0) :
> + (tcp_in_initial_slowstart(tp) ? -1 :
> + tp->snd_ssthresh));
> }
>
> static void get_timewait4_sock(const struct inet_timewait_sock *tw,
> @@ -2695,11 +2694,10 @@ static void get_timewait4_sock(const struct inet_timewait_sock *tw,
> destp = ntohs(tw->tw_dport);
> srcp = ntohs(tw->tw_sport);
>
> - seq_printf(f, "%4d: %08X:%04X %08X:%04X"
> - " %02X %08X:%08X %02X:%08lX %08X %5d %8d %d %d %pK%n",
> - i, src, srcp, dest, destp, tw->tw_substate, 0, 0,
> - 3, jiffies_delta_to_clock_t(delta), 0, 0, 0, 0,
> - atomic_read(&tw->tw_refcnt), tw, len);
> + *len = seq_printf(f, "%4d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX %08X %5d %8d %d %d %pK",
> + i, src, srcp, dest, destp, tw->tw_substate, 0, 0,
> + 3, jiffies_delta_to_clock_t(delta), 0, 0, 0, 0,
> + atomic_read(&tw->tw_refcnt), tw);
> }
>
> #define TMPSZ 150
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index 74d2c95..ddc24a2d 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -2158,16 +2158,15 @@ static void udp4_format_sock(struct sock *sp, struct seq_file *f,
> __u16 destp = ntohs(inet->inet_dport);
> __u16 srcp = ntohs(inet->inet_sport);
>
> - seq_printf(f, "%5d: %08X:%04X %08X:%04X"
> - " %02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %d%n",
> - bucket, src, srcp, dest, destp, sp->sk_state,
> - sk_wmem_alloc_get(sp),
> - sk_rmem_alloc_get(sp),
> - 0, 0L, 0,
> - from_kuid_munged(seq_user_ns(f), sock_i_uid(sp)),
> - 0, sock_i_ino(sp),
> - atomic_read(&sp->sk_refcnt), sp,
> - atomic_read(&sp->sk_drops), len);
> + *len = seq_printf(f, "%5d: %08X:%04X %08X:%04X %02X %08X:%08X %02X:%08lX %08X %5u %8d %lu %d %pK %d",
> + bucket, src, srcp, dest, destp, sp->sk_state,
> + sk_wmem_alloc_get(sp),
> + sk_rmem_alloc_get(sp),
> + 0, 0L, 0,
> + from_kuid_munged(seq_user_ns(f), sock_i_uid(sp)),
> + 0, sock_i_ino(sp),
> + atomic_read(&sp->sk_refcnt), sp,
> + atomic_read(&sp->sk_drops));
> }
>
> int udp4_seq_show(struct seq_file *seq, void *v)
> diff --git a/net/phonet/socket.c b/net/phonet/socket.c
> index 77e38f7..553f896 100644
> --- a/net/phonet/socket.c
> +++ b/net/phonet/socket.c
> @@ -598,21 +598,20 @@ static int pn_sock_seq_show(struct seq_file *seq, void *v)
> int len;
>
> if (v == SEQ_START_TOKEN)
> - seq_printf(seq, "%s%n", "pt loc rem rs st tx_queue rx_queue "
> - " uid inode ref pointer drops", &len);
> + len = seq_puts(seq, "pt loc rem rs st tx_queue rx_queue uid inode ref pointer drops");
> else {
> struct sock *sk = v;
> struct pn_sock *pn = pn_sk(sk);
>
> - seq_printf(seq, "%2d %04X:%04X:%02X %02X %08X:%08X %5d %lu "
> - "%d %pK %d%n",
> - sk->sk_protocol, pn->sobject, pn->dobject,
> - pn->resource, sk->sk_state,
> - sk_wmem_alloc_get(sk), sk_rmem_alloc_get(sk),
> - from_kuid_munged(seq_user_ns(seq), sock_i_uid(sk)),
> - sock_i_ino(sk),
> - atomic_read(&sk->sk_refcnt), sk,
> - atomic_read(&sk->sk_drops), &len);
> + len = seq_printf(seq, "%2d %04X:%04X:%02X %02X %08X:%08X %5d %lu %d %pK %d",
> + sk->sk_protocol, pn->sobject, pn->dobject,
> + pn->resource, sk->sk_state,
> + sk_wmem_alloc_get(sk), sk_rmem_alloc_get(sk),
> + from_kuid_munged(seq_user_ns(seq),
> + sock_i_uid(sk)),
> + sock_i_ino(sk),
> + atomic_read(&sk->sk_refcnt), sk,
> + atomic_read(&sk->sk_drops));
> }
> seq_printf(seq, "%*s\n", 127 - len, "");
> return 0;
> @@ -788,15 +787,16 @@ static int pn_res_seq_show(struct seq_file *seq, void *v)
> int len;
>
> if (v == SEQ_START_TOKEN)
> - seq_printf(seq, "%s%n", "rs uid inode", &len);
> + len = seq_puts(seq, "rs uid inode");
> else {
> struct sock **psk = v;
> struct sock *sk = *psk;
>
> - seq_printf(seq, "%02X %5u %lu%n",
> - (int) (psk - pnres.sk),
> - from_kuid_munged(seq_user_ns(seq), sock_i_uid(sk)),
> - sock_i_ino(sk), &len);
> + len = seq_printf(seq, "%02X %5u %lu",
> + (int) (psk - pnres.sk),
> + from_kuid_munged(seq_user_ns(seq),
> + sock_i_uid(sk)),
> + sock_i_ino(sk));
> }
> seq_printf(seq, "%*s\n", 63 - len, "");
> return 0;
> diff --git a/net/sctp/objcnt.c b/net/sctp/objcnt.c
> index 5ea573b..8034325 100644
> --- a/net/sctp/objcnt.c
> +++ b/net/sctp/objcnt.c
> @@ -82,8 +82,9 @@ static int sctp_objcnt_seq_show(struct seq_file *seq, void *v)
> int i, len;
>
> i = (int)*(loff_t *)v;
> - seq_printf(seq, "%s: %d%n", sctp_dbg_objcnt[i].label,
> - atomic_read(sctp_dbg_objcnt[i].counter), &len);
> + len = seq_printf(seq, "%s: %d",
> + sctp_dbg_objcnt[i].label,
> + atomic_read(sctp_dbg_objcnt[i].counter));
> seq_printf(seq, "%*s\n", 127 - len, "");
> return 0;
> }
> --
> 1.8.1.2.459.gbcd45b4.dirty
>
>
>
--
Kees Cook
Chrome OS Security
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