gfs2: Validate i_depth for exhash directories

Vulnerability Description

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://git.kernel.org/stable/c/076e992752e4b24178918f748d75597c80a408d2
• https://git.kernel.org/stable/c/366183911b153e9b8cf758e1414e1154d7569337
• https://git.kernel.org/stable/c/112bb60cd0e254a369e95aa9941a694ffeca089f
• https://git.kernel.org/stable/c/cddea0c721106ea480371412d8de21705eb27376
• https://git.kernel.org/stable/c/53a0249d68a210c16e961b83adfa82f94ee0a53d
• https://git.kernel.org/stable/c/b5f46951e62377b6e406fadc18bc3c5bdf1632a7
• https://git.kernel.org/stable/c/9680c58675b82348ab84d387e4fa727f7587e1a0
• https://git.kernel.org/stable/c/557c024ca7250bb65ae60f16c02074106c2f197b