1) lift NUL-termination into the callers
2) pass pointer to the end of buffer instead of that to beginning.
(1) allows to simplify dentry_path() - we don't need to play silly
games with restoring the leading / of "//deleted" after __dentry_path()
would've overwritten it with NUL.
We also do not need to check if (either) prepend() in there fails -
if the buffer is not large enough, we'll end with negative buflen
after prepend() and __dentry_path() will return the right value
(ERR_PTR(-ENAMETOOLONG)) just fine.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Fix data race in prepend_path() with re-reading mnt->mnt_ns twice
without holding the lock.
is_mounted() does check for NULL, but is_anon_ns(mnt->mnt_ns) might
re-read the pointer again which could be NULL already, if in between
reads one of kern_unmount()/kern_unmount_array()/umount_tree() sets
mnt->mnt_ns to NULL.
This is seen in production with the following stack trace:
BUG: kernel NULL pointer dereference, address: 0000000000000048
...
RIP: 0010:prepend_path.isra.4+0x1ce/0x2e0
Call Trace:
d_path+0xe6/0x150
proc_pid_readlink+0x8f/0x100
vfs_readlink+0xf8/0x110
do_readlinkat+0xfd/0x120
__x64_sys_readlinkat+0x1a/0x20
do_syscall_64+0x42/0x110
entry_SYSCALL_64_after_hwframe+0x44/0xa9
Fixes: f2683bd8d5 ("[PATCH] fix d_absolute_path() interplay with fsmount()")
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
