On Fri, 13 May 2022 10:52:25 +0800 Luo Meng <luomeng12@xxxxxxxxxx> wrote:
> When shmem_reconfigure() calls __percpu_counter_compare(), the second
> parameter is unsigned int.
Actually unsigned long long.
> But when define __percpu_counter_compare(),
> the second parameter is signed int.
Actually s64.
> So the abs of count - rhs, UBSAN shows the following warning:
>
Here's my amended paragraph:
: When shmem_reconfigure() calls __percpu_counter_compare(), the second
: parameter is unsigned long long. But in the definition of
: __percpu_counter_compare(), the second parameter is s64. So when
: __percpu_counter_compare() executes abs(count - rhs), UBSAN shows the
: following warning:
> ...
>
> Signed-off-by: Luo Meng <luomeng12@xxxxxxxxxx>
> ---
> mm/shmem.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/mm/shmem.c b/mm/shmem.c
> index 4b2fea33158e..15733c480318 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -3487,6 +3487,10 @@ static int shmem_reconfigure(struct fs_context *fc)
>
> raw_spin_lock(&sbinfo->stat_lock);
> inodes = sbinfo->max_inodes - sbinfo->free_inodes;
> + if (ctx->blocks > S64_MAX) {
> + err = "The number of blocks too large";
Should be "is too large". But to match the other error messages'
style, we can use simply "Number of blocks too large".
> + goto out;
> + }
> if ((ctx->seen & SHMEM_SEEN_BLOCKS) && ctx->blocks) {
> if (!sbinfo->max_blocks) {
> err = "Cannot retroactively limit size";
I suppose that's a reasonable fix. I prefer "get the darned types
right" but shmem_options.blocks should be unsigned (can't have a
negative block count) and changing percpu_counter() would be tough.
--- a/mm/shmem.c~tmpfs-fix-undefined-behaviour-in-shmem_reconfigure-fix
+++ a/mm/shmem.c
@@ -3477,7 +3477,7 @@ static int shmem_reconfigure(struct fs_c
raw_spin_lock(&sbinfo->stat_lock);
inodes = sbinfo->max_inodes - sbinfo->free_inodes;
if (ctx->blocks > S64_MAX) {
- err = "The number of blocks too large";
+ err = "Number of blocks too large";
goto out;
}
if ((ctx->seen & SHMEM_SEEN_BLOCKS) && ctx->blocks) {
_
