[PATCH v2] squashfs: Add dictionary size range check to prevent shift-out-of-bounds

[PATCH v2] squashfs: Add dictionary size range check to prevent shift-out-of-bounds

[Ran Hongyun]

When an abnormal SquashFS image (COMP_OPTS flag is 1 but dictionary size
is 0) is mounted, and performs shift operations using dictionarysize, the
shift exponent is -1, causing a shift-out-of-bounds.

Detail as below:
squashfs_comp_opts(msblk, buffer, length)
  squashfs_xz_comp_opts()
    if (comp_opts)
      n = ffs(opts->dict_size) - 1;<----opts->dict_size=0, n=-1
      if (opts->dict_size != (1 << n) && opts->dict_size !=
	  	(1 << n) + (1 << (n + 1))) <----shift-out-of-bounds

Fix it by adding a dictionary size range check before the shift operation.

Fixes: ff750311d30a ("Squashfs: add compression options support to xz decompressor")
Signed-off-by: Ran Hongyun <ranhongyun1@huawei.com>
---
 fs/squashfs/xz_wrapper.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/squashfs/xz_wrapper.c b/fs/squashfs/xz_wrapper.c
index 6c49481a2f8c..7d54cd524d6d 100644
--- a/fs/squashfs/xz_wrapper.c
+++ b/fs/squashfs/xz_wrapper.c
@@ -57,10 +57,10 @@ static void *squashfs_xz_comp_opts(struct squashfs_sb_info *msblk,
 
 		opts->dict_size = le32_to_cpu(comp_opts->dictionary_size);
 
-		/* the dictionary size should be 2^n or 2^n+2^(n+1) */
+		/* the dictionary size should be positive and 2^n or 2^n+2^(n+1) */
 		n = ffs(opts->dict_size) - 1;
-		if (opts->dict_size != (1 << n) && opts->dict_size != (1 << n) +
-						(1 << (n + 1))) {
+		if (opts->dict_size <= 0 || (opts->dict_size != (1 << n) &&
+			opts->dict_size != (1 << n) + (1 << (n + 1)))) {
 			err = -EIO;
 			goto out;
 		}
-- 
2.52.0

Re: [PATCH v2] squashfs: Add dictionary size range check to prevent shift-out-of-bounds

[Zhihao Cheng]

在 2026/7/13 19:55, Ran Hongyun 写道:
> When an abnormal SquashFS image (COMP_OPTS flag is 1 but dictionary size
> is 0) is mounted, and performs shift operations using dictionarysize, the
> shift exponent is -1, causing a shift-out-of-bounds.
> 
> Detail as below:
> squashfs_comp_opts(msblk, buffer, length)
>    squashfs_xz_comp_opts()
>      if (comp_opts)
>        n = ffs(opts->dict_size) - 1;<----opts->dict_size=0, n=-1
>        if (opts->dict_size != (1 << n) && opts->dict_size !=
> 	  	(1 << n) + (1 << (n + 1))) <----shift-out-of-bounds
> 
> Fix it by adding a dictionary size range check before the shift operation.
> 
> Fixes: ff750311d30a ("Squashfs: add compression options support to xz decompressor")
> Signed-off-by: Ran Hongyun <ranhongyun1@huawei.com>
> ---
>   fs/squashfs/xz_wrapper.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)

Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
> 
> diff --git a/fs/squashfs/xz_wrapper.c b/fs/squashfs/xz_wrapper.c
> index 6c49481a2f8c..7d54cd524d6d 100644
> --- a/fs/squashfs/xz_wrapper.c
> +++ b/fs/squashfs/xz_wrapper.c
> @@ -57,10 +57,10 @@ static void *squashfs_xz_comp_opts(struct squashfs_sb_info *msblk,
>   
>   		opts->dict_size = le32_to_cpu(comp_opts->dictionary_size);
>   
> -		/* the dictionary size should be 2^n or 2^n+2^(n+1) */
> +		/* the dictionary size should be positive and 2^n or 2^n+2^(n+1) */
>   		n = ffs(opts->dict_size) - 1;
> -		if (opts->dict_size != (1 << n) && opts->dict_size != (1 << n) +
> -						(1 << (n + 1))) {
> +		if (opts->dict_size <= 0 || (opts->dict_size != (1 << n) &&
> +			opts->dict_size != (1 << n) + (1 << (n + 1)))) {
>   			err = -EIO;
>   			goto out;
>   		}
> 

Re: [PATCH v2] squashfs: Add dictionary size range check to prevent shift-out-of-bounds

[Phillip Lougher]

On 13/07/2026 12:55, Ran Hongyun wrote:
> When an abnormal SquashFS image (COMP_OPTS flag is 1 but dictionary size
> is 0) is mounted, and performs shift operations using dictionarysize, the
> shift exponent is -1, causing a shift-out-of-bounds.
> 
> Detail as below:
> squashfs_comp_opts(msblk, buffer, length)
>    squashfs_xz_comp_opts()
>      if (comp_opts)
>        n = ffs(opts->dict_size) - 1;<----opts->dict_size=0, n=-1
>        if (opts->dict_size != (1 << n) && opts->dict_size !=
> 	  	(1 << n) + (1 << (n + 1))) <----shift-out-of-bounds
> 
> Fix it by adding a dictionary size range check before the shift operation.

Reviewed-by: Phillip Lougher <phillip@squashfs.org.uk>

Andrew Morton handles patch submission to Linus for me.  CC'ing him.

Phillip

Re: [PATCH 0/2] lockd: fix two bugs on nlmclnt_find_lockowner() failure path

[Ran Hongyun]

Friendly ping.

Re: [PATCH v2] squashfs: Add dictionary size range check to prevent shift-out-of-bounds

[Christian Brauner]

On Mon, 13 Jul 2026 19:55:25 +0800, Ran Hongyun wrote:
> When an abnormal SquashFS image (COMP_OPTS flag is 1 but dictionary size
> is 0) is mounted, and performs shift operations using dictionarysize, the
> shift exponent is -1, causing a shift-out-of-bounds.
> 
> Detail as below:
> squashfs_comp_opts(msblk, buffer, length)
>   squashfs_xz_comp_opts()
>     if (comp_opts)
>       n = ffs(opts->dict_size) - 1;<----opts->dict_size=0, n=-1
>       if (opts->dict_size != (1 << n) && opts->dict_size !=
> 	  	(1 << n) + (1 << (n + 1))) <----shift-out-of-bounds
> 
> [...]

Applied to the vfs.fixes branch of the vfs/vfs.git tree.
Patches in the vfs.fixes branch should appear in linux-next soon.

Please report any outstanding bugs that were missed during review in a
new review to the original patch series allowing us to drop it.

It's encouraged to provide Acked-bys and Reviewed-bys even though the
patch has now been applied. If possible patch trailers will be updated.

Note that commit hashes shown below are subject to change due to rebase,
trailer updates or similar. If in doubt, please check the listed branch.

tree:   https://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs.git
branch: vfs.fixes

[1/1] squashfs: Add dictionary size range check to prevent shift-out-of-bounds
      https://git.kernel.org/vfs/vfs/c/1f7745fb3580

Re: [PATCH v2] squashfs: Add dictionary size range check to prevent shift-out-of-bounds

[Ran Hongyun]

Thanks for the update!