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: ff750311d3 ("Squashfs: add compression options support to xz decompressor")
Signed-off-by: Ran Hongyun <ranhongyun1@huawei.com>
Link: https://patch.msgid.link/20260713115525.2661734-1-ranhongyun1@huawei.com
Reviewed-by: Phillip Lougher <phillip@squashfs.org.uk>
Reviewed-by: Zhihao Cheng <chengzhihao1@huawei.com>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>
1f7745fb35