In the Linux kernel, the following vulnerability has been resolved:

gfs2: Validate i_depth for exhash directories

A fuzzer test introduced corruption that ends up with a depth of 0 in
dir_e_read(), causing an undefined shift by 32 at:

index = hash >> (32 - dip->i_depth);

As calculated in an open-coded way in dir_make_exhash(), the minimum
depth for an exhash directory is ilog2(sdp->sd_hash_ptrs) and 0 is
invalid as sdp->sd_hash_ptrs is fixed as sdp->bsize / 16 at mount time.

So we can avoid the undefined behaviour by checking for depth values
lower than the minimum in gfs2_dinode_in(). Values greater than the
maximum are already being checked for there.

Also switch the calculation in dir_make_exhash() to use ilog2() to
clarify how the depth is calculated.

Tested with the syzkaller repro.c and xfstests '-g quick'.

References

• https://nvd.nist.gov/vuln/detail/CVE-2025-38710
• https://git.kernel.org/stable/c/53a0249d68a210c16e961b83adfa82f94ee0a53d
• https://git.kernel.org/stable/c/557c024ca7250bb65ae60f16c02074106c2f197b
• https://git.kernel.org/stable/c/9680c58675b82348ab84d387e4fa727f7587e1a0
• https://git.kernel.org/stable/c/b5f46951e62377b6e406fadc18bc3c5bdf1632a7