[PATCH] Btrfs: fix null pointer dereference on compressed write path error

[PATCH] Btrfs: fix null pointer dereference on compressed write path error

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

At inode.c:compress_file_range(), under the "free_pages_out" label, we can
end up dereferencing the "pages" pointer when it has a NULL value. This
case happens when "start" has a value of 0 and we fail to allocate memory
for the "pages" pointer. When that happens we jump to the "cont" label and
then enter the "if (start == 0)" branch where we immediately call the
cow_file_range_inline() function. If that function returns an error (like
-ENOMEM for example) we jump to the "free_pages_out" label and then access
"pages[i]" leading to a NULL pointer dereference, since "nr_pages" has a
value greater than zero at that point.

Fix this by setting "nr_pages" to 0 when we fail to allocate memory for
the "pages" pointer.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201119
Fixes: 771ed689d2cd ("Btrfs: Optimize compressed writeback and reads")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---
 fs/btrfs/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 66c6c4103d2f..d6b61b1facdd 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -503,6 +503,7 @@ static noinline void compress_file_range(struct inode *inode,
 		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
 		if (!pages) {
 			/* just bail out to the uncompressed code */
+			nr_pages = 0;
 			goto cont;
 		}
 
-- 
2.11.0

[PATCH v2] Btrfs: fix null pointer dereference on compressed write path error

[fdmanana]

From: Filipe Manana <fdmanana@suse.com>

At inode.c:compress_file_range(), under the "free_pages_out" label, we can
end up dereferencing the "pages" pointer when it has a NULL value. This
case happens when "start" has a value of 0 and we fail to allocate memory
for the "pages" pointer. When that happens we jump to the "cont" label and
then enter the "if (start == 0)" branch where we immediately call the
cow_file_range_inline() function. If that function returns 0 (success
creating an inline extent) or an error (like -ENOMEM for example) we jump
to the "free_pages_out" label and then access "pages[i]" leading to a NULL
pointer dereference, since "nr_pages" has a value greater than zero at
that point.

Fix this by setting "nr_pages" to 0 when we fail to allocate memory for
the "pages" pointer.

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201119
Fixes: 771ed689d2cd ("Btrfs: Optimize compressed writeback and reads")
Signed-off-by: Filipe Manana <fdmanana@suse.com>
---

V2: Updated changelog.

 fs/btrfs/inode.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 66c6c4103d2f..d6b61b1facdd 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -503,6 +503,7 @@ static noinline void compress_file_range(struct inode *inode,
 		pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
 		if (!pages) {
 			/* just bail out to the uncompressed code */
+			nr_pages = 0;
 			goto cont;
 		}
 
-- 
2.11.0

Re: [PATCH v2] Btrfs: fix null pointer dereference on compressed write path error

[Liu Bo]

On Fri, Oct 12, 2018 at 4:38 PM <fdmanana@kernel.org> wrote:
>
> From: Filipe Manana <fdmanana@suse.com>
>
> At inode.c:compress_file_range(), under the "free_pages_out" label, we can
> end up dereferencing the "pages" pointer when it has a NULL value. This
> case happens when "start" has a value of 0 and we fail to allocate memory
> for the "pages" pointer. When that happens we jump to the "cont" label and
> then enter the "if (start == 0)" branch where we immediately call the
> cow_file_range_inline() function. If that function returns 0 (success
> creating an inline extent) or an error (like -ENOMEM for example) we jump
> to the "free_pages_out" label and then access "pages[i]" leading to a NULL
> pointer dereference, since "nr_pages" has a value greater than zero at
> that point.
>
> Fix this by setting "nr_pages" to 0 when we fail to allocate memory for
> the "pages" pointer.
>

Looks good.

Reviewed-by: Liu Bo <bo.liu@linux.alibaba.com>

thanks,
liubo

> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201119
> Fixes: 771ed689d2cd ("Btrfs: Optimize compressed writeback and reads")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>
> ---
>
> V2: Updated changelog.
>
>  fs/btrfs/inode.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index 66c6c4103d2f..d6b61b1facdd 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -503,6 +503,7 @@ static noinline void compress_file_range(struct inode *inode,
>                 pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
>                 if (!pages) {
>                         /* just bail out to the uncompressed code */
> +                       nr_pages = 0;
>                         goto cont;
>                 }
>
> --
> 2.11.0
>

Re: [PATCH v2] Btrfs: fix null pointer dereference on compressed write path error

[David Sterba]

On Sat, Oct 13, 2018 at 12:37:25AM +0100, fdmanana@kernel.org wrote:
> From: Filipe Manana <fdmanana@suse.com>
> 
> At inode.c:compress_file_range(), under the "free_pages_out" label, we can
> end up dereferencing the "pages" pointer when it has a NULL value. This
> case happens when "start" has a value of 0 and we fail to allocate memory
> for the "pages" pointer. When that happens we jump to the "cont" label and
> then enter the "if (start == 0)" branch where we immediately call the
> cow_file_range_inline() function. If that function returns 0 (success
> creating an inline extent) or an error (like -ENOMEM for example) we jump
> to the "free_pages_out" label and then access "pages[i]" leading to a NULL
> pointer dereference, since "nr_pages" has a value greater than zero at
> that point.
> 
> Fix this by setting "nr_pages" to 0 when we fail to allocate memory for
> the "pages" pointer.
> 
> Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=201119
> Fixes: 771ed689d2cd ("Btrfs: Optimize compressed writeback and reads")
> Signed-off-by: Filipe Manana <fdmanana@suse.com>

Added to misc-next, thanks.