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authorEric Biggers <ebiggers@google.com>2018-02-06 15:42:08 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2018-02-06 18:32:48 -0800
commitf7340761812fc10313e6fcc115e0bc4f7a799112 (patch)
tree2374b679e8378f22800e233b0c69883546616138
parentc4fed5a91fadc8a277b1eda474317b501651dd3e (diff)
downloadlinux-f7340761812fc10313e6fcc115e0bc4f7a799112.tar.bz2
pipe: read buffer limits atomically
The pipe buffer limits are accessed without any locking, and may be changed at any time by the sysctl handlers. In theory this could cause problems for expressions like the following: pipe_user_pages_hard && user_bufs > pipe_user_pages_hard ... since the assembly code might reference the 'pipe_user_pages_hard' memory location multiple times, and if the admin removes the limit by setting it to 0, there is a very brief window where processes could incorrectly observe the limit to be exceeded. Fix this by loading the limits with READ_ONCE() prior to use. Link: http://lkml.kernel.org/r/20180111052902.14409-8-ebiggers3@gmail.com Signed-off-by: Eric Biggers <ebiggers@google.com> Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Joe Lawrence <joe.lawrence@redhat.com> Cc: Alexander Viro <viro@zeniv.linux.org.uk> Cc: Michael Kerrisk <mtk.manpages@gmail.com> Cc: Willy Tarreau <w@1wt.eu> Cc: Mikulas Patocka <mpatocka@redhat.com> Cc: "Luis R . Rodriguez" <mcgrof@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--fs/pipe.c13
1 files changed, 9 insertions, 4 deletions
diff --git a/fs/pipe.c b/fs/pipe.c
index 8be52158c400..0913aed7fd0d 100644
--- a/fs/pipe.c
+++ b/fs/pipe.c
@@ -605,12 +605,16 @@ static unsigned long account_pipe_buffers(struct user_struct *user,
static bool too_many_pipe_buffers_soft(unsigned long user_bufs)
{
- return pipe_user_pages_soft && user_bufs > pipe_user_pages_soft;
+ unsigned long soft_limit = READ_ONCE(pipe_user_pages_soft);
+
+ return soft_limit && user_bufs > soft_limit;
}
static bool too_many_pipe_buffers_hard(unsigned long user_bufs)
{
- return pipe_user_pages_hard && user_bufs > pipe_user_pages_hard;
+ unsigned long hard_limit = READ_ONCE(pipe_user_pages_hard);
+
+ return hard_limit && user_bufs > hard_limit;
}
static bool is_unprivileged_user(void)
@@ -624,13 +628,14 @@ struct pipe_inode_info *alloc_pipe_info(void)
unsigned long pipe_bufs = PIPE_DEF_BUFFERS;
struct user_struct *user = get_current_user();
unsigned long user_bufs;
+ unsigned int max_size = READ_ONCE(pipe_max_size);
pipe = kzalloc(sizeof(struct pipe_inode_info), GFP_KERNEL_ACCOUNT);
if (pipe == NULL)
goto out_free_uid;
- if (pipe_bufs * PAGE_SIZE > pipe_max_size && !capable(CAP_SYS_RESOURCE))
- pipe_bufs = pipe_max_size >> PAGE_SHIFT;
+ if (pipe_bufs * PAGE_SIZE > max_size && !capable(CAP_SYS_RESOURCE))
+ pipe_bufs = max_size >> PAGE_SHIFT;
user_bufs = account_pipe_buffers(user, 0, pipe_bufs);