fsdax: Fix infinite loop in dax_iomap_rw()

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: fsdax: Fix infinite loop in dax_iomap_rw() I got an infinite loop and a WARNING report when executing a tail command in virtiofs. WARNING: CPU: 10 PID: 964 at fs/iomap/iter.c:34 iomap_iter+0x3a2/0x3d0 Modules linked in: CPU: 10 PID: 964 Comm: tail Not tainted 5.19.0-rc7 Call Trace: <TASK> dax_iomap_rw+0xea/0x620 ? __this_cpu_preempt_check+0x13/0x20 fuse_dax_read_iter+0x47/0x80 fuse_file_read_iter+0xae/0xd0 new_sync_read+0xfe/0x180 ? 0xffffffff81000000 vfs_read+0x14d/0x1a0 ksys_read+0x6d/0xf0 __x64_sys_read+0x1a/0x20 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x63/0xcd The tail command will call read() with a count of 0. In this case, iomap_iter() will report this WARNING, and always return 1 which casuing the infinite loop in dax_iomap_rw(). Fixing by checking count whether is 0 in dax_iomap_rw().

References

• https://git.kernel.org/stable/c/463f36137c40342fb03bba380c1bf703c40d89a6
• https://git.kernel.org/stable/c/929ef155e1da41c06f4d8ca86ae12b851a83a744
• https://git.kernel.org/stable/c/60644dffac87b1bb47bdb393aa29d5f2ffcf41a0
• https://git.kernel.org/stable/c/17d9c15c9b9e7fb285f7ac5367dfb5f00ff575e3