* [PATCH] btrfs: zoned: fix uninitialized max_chunk_size
@ 2021-03-23 12:46 Arnd Bergmann
2021-03-23 13:23 ` David Sterba
0 siblings, 1 reply; 2+ messages in thread
From: Arnd Bergmann @ 2021-03-23 12:46 UTC (permalink / raw)
To: Chris Mason, Josef Bacik, David Sterba, Anand Jain, Naohiro Aota
Cc: Arnd Bergmann, Nikolay Borisov, Johannes Thumshirn, linux-btrfs,
linux-kernel
From: Arnd Bergmann <arnd@arndb.de>
The ctl->max_chunk_size member might be used uninitialized
when none of the three conditions for initializing it in
init_alloc_chunk_ctl_policy_zoned() are true:
In function ‘init_alloc_chunk_ctl_policy_zoned’,
inlined from ‘init_alloc_chunk_ctl’ at fs/btrfs/volumes.c:5023:3,
inlined from ‘btrfs_alloc_chunk’ at fs/btrfs/volumes.c:5340:2:
include/linux/compiler-gcc.h:48:45: error: ‘ctl.max_chunk_size’ may be used uninitialized [-Werror=maybe-uninitialized]
4998 | ctl->max_chunk_size = min(limit, ctl->max_chunk_size);
| ^~~
fs/btrfs/volumes.c: In function ‘btrfs_alloc_chunk’:
fs/btrfs/volumes.c:5316:32: note: ‘ctl’ declared here
5316 | struct alloc_chunk_ctl ctl;
| ^~~
Initialize it to UINT_MAX and rely on the min() expression to limit
it.
Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
Note that the -Wmaybe-unintialized warning is globally disabled
by default. For some reason I got this warning anyway when building
this specific file with gcc-11.
---
fs/btrfs/volumes.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index bc3b33efddc5..b42b423b6a10 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -4980,6 +4980,7 @@ static void init_alloc_chunk_ctl_policy_zoned(
u64 type = ctl->type;
ctl->max_stripe_size = zone_size;
+ ctl->max_chunk_size = UINT_MAX;
if (type & BTRFS_BLOCK_GROUP_DATA) {
ctl->max_chunk_size = round_down(BTRFS_MAX_DATA_CHUNK_SIZE,
zone_size);
--
2.29.2
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] btrfs: zoned: fix uninitialized max_chunk_size
2021-03-23 12:46 [PATCH] btrfs: zoned: fix uninitialized max_chunk_size Arnd Bergmann
@ 2021-03-23 13:23 ` David Sterba
0 siblings, 0 replies; 2+ messages in thread
From: David Sterba @ 2021-03-23 13:23 UTC (permalink / raw)
To: Arnd Bergmann
Cc: Chris Mason, Josef Bacik, David Sterba, Anand Jain, Naohiro Aota,
Arnd Bergmann, Nikolay Borisov, Johannes Thumshirn, linux-btrfs,
linux-kernel
On Tue, Mar 23, 2021 at 01:46:19PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
>
> The ctl->max_chunk_size member might be used uninitialized
> when none of the three conditions for initializing it in
> init_alloc_chunk_ctl_policy_zoned() are true:
>
> In function ‘init_alloc_chunk_ctl_policy_zoned’,
> inlined from ‘init_alloc_chunk_ctl’ at fs/btrfs/volumes.c:5023:3,
> inlined from ‘btrfs_alloc_chunk’ at fs/btrfs/volumes.c:5340:2:
> include/linux/compiler-gcc.h:48:45: error: ‘ctl.max_chunk_size’ may be used uninitialized [-Werror=maybe-uninitialized]
> 4998 | ctl->max_chunk_size = min(limit, ctl->max_chunk_size);
> | ^~~
> fs/btrfs/volumes.c: In function ‘btrfs_alloc_chunk’:
> fs/btrfs/volumes.c:5316:32: note: ‘ctl’ declared here
> 5316 | struct alloc_chunk_ctl ctl;
> | ^~~
>
> Initialize it to UINT_MAX and rely on the min() expression to limit
> it.
>
> Fixes: 1cd6121f2a38 ("btrfs: zoned: implement zoned chunk allocator")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> Note that the -Wmaybe-unintialized warning is globally disabled
> by default. For some reason I got this warning anyway when building
> this specific file with gcc-11.
The warning catches a theoretical case but this would not happen in
pracitce. There are three bits to check and that covers all valid
options, but there should be a final else {} like is in
init_alloc_chunk_ctl_policy_regular that does not let the function
continue as that would mean there are worse problems.
btrfs_alloc_chunk
init_alloc_chunk_ctl
init_alloc_chunk_ctl_policy_zoned
and btrfs_alloc_chunk validates the ctl->flags against
BTRFS_BLOCK_GROUP_TYPE_MASK, which is exactly the tree branches.
> ---
> fs/btrfs/volumes.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index bc3b33efddc5..b42b423b6a10 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -4980,6 +4980,7 @@ static void init_alloc_chunk_ctl_policy_zoned(
> u64 type = ctl->type;
>
> ctl->max_stripe_size = zone_size;
> + ctl->max_chunk_size = UINT_MAX;
This would allow the min() work but otherwise is not an expected to
happen at all.
> if (type & BTRFS_BLOCK_GROUP_DATA) {
> ctl->max_chunk_size = round_down(BTRFS_MAX_DATA_CHUNK_SIZE,
> zone_size);
> --
> 2.29.2
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2021-03-23 12:46 [PATCH] btrfs: zoned: fix uninitialized max_chunk_size Arnd Bergmann
2021-03-23 13:23 ` David Sterba
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