jfs: nlink overflow in jfs_rename

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: jfs: nlink overflow in jfs_rename If nlink is maximal for a directory (-1) and inside that directory you perform a rename for some child directory (not moving from the parent), then the nlink of the first directory is first incremented and later decremented. Normally this is fine, but when nlink = -1 this causes a wrap around to 0, and then drop_nlink issues a warning. After applying the patch syzbot no longer issues any warnings. I also ran some basic fs tests to look for any regressions.

References

• https://git.kernel.org/stable/c/2108829a59f081e822fdab8c2cd7131deb8aa8a1
• https://git.kernel.org/stable/c/b4330a0d0947fbdc9d445cbbeabd8cc910a8c9ca
• https://git.kernel.org/stable/c/a3d66089e50a6e0142f8884471f74292102ea9aa
• https://git.kernel.org/stable/c/f70fcbc2ac7c24f087a2c895c5753aa730b1e479
• https://git.kernel.org/stable/c/5d77c36cd4b698649f5c30c5f6c084f4f61d1880
• https://git.kernel.org/stable/c/fe136426e30ca6debcf916fd6a141555ed9fde74
• https://git.kernel.org/stable/c/93c325746ae59709b4f9bad4e3e4761c8d566c70
• https://git.kernel.org/stable/c/9218dc26fd922b09858ecd3666ed57dfd8098da8