This is a note to let you know that I've just added the patch titled netfilter: ebtables: compat: reject all padding in matches/watchers to the 4.19-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: netfilter-ebtables-compat-reject-all-padding-in-matc.patch and it can be found in the queue-4.19 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 08266b24c424b81c1cbdc4f2bdeef434e466e758 Author: Florian Westphal <fw@xxxxxxxxx> Date: Sun Dec 15 03:49:25 2019 +0100 netfilter: ebtables: compat: reject all padding in matches/watchers [ Upstream commit e608f631f0ba5f1fc5ee2e260a3a35d13107cbfe ] syzbot reported following splat: BUG: KASAN: vmalloc-out-of-bounds in size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline] BUG: KASAN: vmalloc-out-of-bounds in compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155 Read of size 4 at addr ffffc900004461f4 by task syz-executor267/7937 CPU: 1 PID: 7937 Comm: syz-executor267 Not tainted 5.5.0-rc1-syzkaller #0 size_entry_mwt net/bridge/netfilter/ebtables.c:2063 [inline] compat_copy_entries+0x128b/0x1380 net/bridge/netfilter/ebtables.c:2155 compat_do_replace+0x344/0x720 net/bridge/netfilter/ebtables.c:2249 compat_do_ebt_set_ctl+0x22f/0x27e net/bridge/netfilter/ebtables.c:2333 [..] Because padding isn't considered during computation of ->buf_user_offset, "total" is decremented by fewer bytes than it should. Therefore, the first part of if (*total < sizeof(*entry) || entry->next_offset < sizeof(*entry)) will pass, -- it should not have. This causes oob access: entry->next_offset is past the vmalloced size. Reject padding and check that computed user offset (sum of ebt_entry structure plus all individual matches/watchers/targets) is same value that userspace gave us as the offset of the next entry. Reported-by: syzbot+f68108fed972453a0ad4@xxxxxxxxxxxxxxxxxxxxxxxxx Fixes: 81e675c227ec ("netfilter: ebtables: add CONFIG_COMPAT support") Signed-off-by: Florian Westphal <fw@xxxxxxxxx> Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c index 7d249afa1466..785e19afd6aa 100644 --- a/net/bridge/netfilter/ebtables.c +++ b/net/bridge/netfilter/ebtables.c @@ -1876,7 +1876,7 @@ static int ebt_buf_count(struct ebt_entries_buf_state *state, unsigned int sz) } static int ebt_buf_add(struct ebt_entries_buf_state *state, - void *data, unsigned int sz) + const void *data, unsigned int sz) { if (state->buf_kern_start == NULL) goto count_only; @@ -1910,7 +1910,7 @@ enum compat_mwt { EBT_COMPAT_TARGET, }; -static int compat_mtw_from_user(struct compat_ebt_entry_mwt *mwt, +static int compat_mtw_from_user(const struct compat_ebt_entry_mwt *mwt, enum compat_mwt compat_mwt, struct ebt_entries_buf_state *state, const unsigned char *base) @@ -1988,22 +1988,23 @@ static int compat_mtw_from_user(struct compat_ebt_entry_mwt *mwt, /* return size of all matches, watchers or target, including necessary * alignment and padding. */ -static int ebt_size_mwt(struct compat_ebt_entry_mwt *match32, +static int ebt_size_mwt(const struct compat_ebt_entry_mwt *match32, unsigned int size_left, enum compat_mwt type, struct ebt_entries_buf_state *state, const void *base) { + const char *buf = (const char *)match32; int growth = 0; - char *buf; if (size_left == 0) return 0; - buf = (char *) match32; - - while (size_left >= sizeof(*match32)) { + do { struct ebt_entry_match *match_kern; int ret; + if (size_left < sizeof(*match32)) + return -EINVAL; + match_kern = (struct ebt_entry_match *) state->buf_kern_start; if (match_kern) { char *tmp; @@ -2040,22 +2041,18 @@ static int ebt_size_mwt(struct compat_ebt_entry_mwt *match32, if (match_kern) match_kern->match_size = ret; - /* rule should have no remaining data after target */ - if (type == EBT_COMPAT_TARGET && size_left) - return -EINVAL; - match32 = (struct compat_ebt_entry_mwt *) buf; - } + } while (size_left); return growth; } /* called for all ebt_entry structures. */ -static int size_entry_mwt(struct ebt_entry *entry, const unsigned char *base, +static int size_entry_mwt(const struct ebt_entry *entry, const unsigned char *base, unsigned int *total, struct ebt_entries_buf_state *state) { - unsigned int i, j, startoff, new_offset = 0; + unsigned int i, j, startoff, next_expected_off, new_offset = 0; /* stores match/watchers/targets & offset of next struct ebt_entry: */ unsigned int offsets[4]; unsigned int *offsets_update = NULL; @@ -2141,11 +2138,13 @@ static int size_entry_mwt(struct ebt_entry *entry, const unsigned char *base, return ret; } - startoff = state->buf_user_offset - startoff; + next_expected_off = state->buf_user_offset - startoff; + if (next_expected_off != entry->next_offset) + return -EINVAL; - if (WARN_ON(*total < startoff)) + if (*total < entry->next_offset) return -EINVAL; - *total -= startoff; + *total -= entry->next_offset; return 0; }