4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Lorenzo Stoakes <lstoakes@xxxxxxxxx> commit 6347e8d5bcce33fc36e651901efefbe2c93a43ef upstream. This removes the 'write' argument from access_remote_vm() and replaces it with 'gup_flags' as use of this function previously silently implied FOLL_FORCE, whereas after this patch callers explicitly pass this flag. We make this explicit as use of FOLL_FORCE can result in surprising behaviour (and hence bugs) within the mm subsystem. Signed-off-by: Lorenzo Stoakes <lstoakes@xxxxxxxxx> Acked-by: Michal Hocko <mhocko@xxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Ben Hutchings <ben.hutchings@xxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- fs/proc/base.c | 19 +++++++++++++------ include/linux/mm.h | 2 +- mm/memory.c | 11 +++-------- mm/nommu.c | 7 +++---- 4 files changed, 20 insertions(+), 19 deletions(-) --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -254,7 +254,7 @@ static ssize_t proc_pid_cmdline_read(str * Inherently racy -- command line shares address space * with code and data. */ - rv = access_remote_vm(mm, arg_end - 1, &c, 1, 0); + rv = access_remote_vm(mm, arg_end - 1, &c, 1, FOLL_FORCE); if (rv <= 0) goto out_free_page; @@ -272,7 +272,8 @@ static ssize_t proc_pid_cmdline_read(str int nr_read; _count = min3(count, len, PAGE_SIZE); - nr_read = access_remote_vm(mm, p, page, _count, 0); + nr_read = access_remote_vm(mm, p, page, _count, + FOLL_FORCE); if (nr_read < 0) rv = nr_read; if (nr_read <= 0) @@ -307,7 +308,8 @@ static ssize_t proc_pid_cmdline_read(str bool final; _count = min3(count, len, PAGE_SIZE); - nr_read = access_remote_vm(mm, p, page, _count, 0); + nr_read = access_remote_vm(mm, p, page, _count, + FOLL_FORCE); if (nr_read < 0) rv = nr_read; if (nr_read <= 0) @@ -356,7 +358,8 @@ skip_argv: bool final; _count = min3(count, len, PAGE_SIZE); - nr_read = access_remote_vm(mm, p, page, _count, 0); + nr_read = access_remote_vm(mm, p, page, _count, + FOLL_FORCE); if (nr_read < 0) rv = nr_read; if (nr_read <= 0) @@ -868,6 +871,7 @@ static ssize_t mem_rw(struct file *file, unsigned long addr = *ppos; ssize_t copied; char *page; + unsigned int flags = FOLL_FORCE; if (!mm) return 0; @@ -880,6 +884,9 @@ static ssize_t mem_rw(struct file *file, if (!atomic_inc_not_zero(&mm->mm_users)) goto free; + if (write) + flags |= FOLL_WRITE; + while (count > 0) { int this_len = min_t(int, count, PAGE_SIZE); @@ -888,7 +895,7 @@ static ssize_t mem_rw(struct file *file, break; } - this_len = access_remote_vm(mm, addr, page, this_len, write); + this_len = access_remote_vm(mm, addr, page, this_len, flags); if (!this_len) { if (!copied) copied = -EIO; @@ -1001,7 +1008,7 @@ static ssize_t environ_read(struct file this_len = min(max_len, this_len); retval = access_remote_vm(mm, (env_start + src), - page, this_len, 0); + page, this_len, FOLL_FORCE); if (retval <= 0) { ret = retval; --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1191,7 +1191,7 @@ static inline int fixup_user_fault(struc extern int access_process_vm(struct task_struct *tsk, unsigned long addr, void *buf, int len, int write); extern int access_remote_vm(struct mm_struct *mm, unsigned long addr, - void *buf, int len, int write); + void *buf, int len, unsigned int gup_flags); long __get_user_pages(struct task_struct *tsk, struct mm_struct *mm, unsigned long start, unsigned long nr_pages, --- a/mm/memory.c +++ b/mm/memory.c @@ -3777,19 +3777,14 @@ static int __access_remote_vm(struct tas * @addr: start address to access * @buf: source or destination buffer * @len: number of bytes to transfer - * @write: whether the access is a write + * @gup_flags: flags modifying lookup behaviour * * The caller must hold a reference on @mm. */ int access_remote_vm(struct mm_struct *mm, unsigned long addr, - void *buf, int len, int write) + void *buf, int len, unsigned int gup_flags) { - unsigned int flags = FOLL_FORCE; - - if (write) - flags |= FOLL_WRITE; - - return __access_remote_vm(NULL, mm, addr, buf, len, flags); + return __access_remote_vm(NULL, mm, addr, buf, len, gup_flags); } /* --- a/mm/nommu.c +++ b/mm/nommu.c @@ -1967,15 +1967,14 @@ static int __access_remote_vm(struct tas * @addr: start address to access * @buf: source or destination buffer * @len: number of bytes to transfer - * @write: whether the access is a write + * @gup_flags: flags modifying lookup behaviour * * The caller must hold a reference on @mm. */ int access_remote_vm(struct mm_struct *mm, unsigned long addr, - void *buf, int len, int write) + void *buf, int len, unsigned int gup_flags) { - return __access_remote_vm(NULL, mm, addr, buf, len, - write ? FOLL_WRITE : 0); + return __access_remote_vm(NULL, mm, addr, buf, len, gup_flags); } /*