Commit f0cc6ffb8ce8961db587e5072168cac0cbc25f05
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Revert "fs: Allow unprivileged linkat(..., AT_EMPTY_PATH) aka flink"
This reverts commit bb2314b47996491bbc5add73633905c3120b6268. It wasn't necessarily wrong per se, but we're still busily discussing the exact details of this all, so I'm going to revert it for now. It's true that you can already do flink() through /proc and that flink() isn't new. But as Brad Spengler points out, some secure environments do not mount proc, and flink adds a new interface that can avoid path lookup of the source for those kinds of environments. We may re-do this (and even mark it for stable backporting back in 3.11 and possibly earlier) once the whole discussion about the interface is done. Cc: Andy Lutomirski <luto@amacapital.net> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Brad Spengler <spender@grsecurity.net> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Showing 1 changed file with 7 additions and 3 deletions Side-by-side Diff
fs/namei.c
| ... | ... | @@ -3671,11 +3671,15 @@ |
| 3671 | 3671 | if ((flags & ~(AT_SYMLINK_FOLLOW | AT_EMPTY_PATH)) != 0) |
| 3672 | 3672 | return -EINVAL; |
| 3673 | 3673 | /* |
| 3674 | - * Using empty names is equivalent to using AT_SYMLINK_FOLLOW | |
| 3675 | - * on /proc/self/fd/<fd>. | |
| 3674 | + * To use null names we require CAP_DAC_READ_SEARCH | |
| 3675 | + * This ensures that not everyone will be able to create | |
| 3676 | + * handlink using the passed filedescriptor. | |
| 3676 | 3677 | */ |
| 3677 | - if (flags & AT_EMPTY_PATH) | |
| 3678 | + if (flags & AT_EMPTY_PATH) { | |
| 3679 | + if (!capable(CAP_DAC_READ_SEARCH)) | |
| 3680 | + return -ENOENT; | |
| 3678 | 3681 | how = LOOKUP_EMPTY; |
| 3682 | + } | |
| 3679 | 3683 | |
| 3680 | 3684 | if (flags & AT_SYMLINK_FOLLOW) |
| 3681 | 3685 | how |= LOOKUP_FOLLOW; |