Messages in this thread | | | From | Andy Lutomirski <> | Date | Mon, 21 Apr 2014 10:04:38 -0700 | Subject | Re: [RFC 2/2] fs,proc: Respect FMODE_WRITE when opening /proc/pid/fd/N |
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On Mon, Apr 21, 2014 at 10:00 AM, Andy Lutomirski <luto@amacapital.net> wrote: > On Mon, Apr 21, 2014 at 9:30 AM, Al Viro <viro@zeniv.linux.org.uk> wrote: >> On Mon, Apr 21, 2014 at 09:22:48AM -0700, Andy Lutomirski wrote: >> >>> +static int proc_may_follow(struct nameidata *nd, struct file *f) >>> +{ >>> + if (!nd) >>> + return 0; /* This is readlink, */ >>> + >>> + if ((nd->flags & LOOKUP_WRITE) && !(f->f_mode & FMODE_WRITE)) >>> + return -EACCES; >>> + >>> + return 0; >>> +} >> >> And this is just plain wrong. WTF are you making the traversal of symlink >> in the middle of pathname dependent on the open flags? > > Can you give me a hint? There are three cases that I need to > distinguish, I think: > > 1. readlink. Currently handled by nd == NULL. It's ugly, and I'll clean it up. > > 2. Traversal in the middle of a path. This can be either literally in > the middle (e.g. "/proc/self/fd/3/something_else") or in a symlink > that's the last component of the literal path (e.g. "fd3null" where > "fd3null" is a symlink to "/proc/self/fd/3/null" and "null" is either > a file or a symlink to /dev/null). I have the latter type wrong in > this patch. > > 3. Actually opening /proc/self/fd/N. This can be direct or by opening > a symlink to /proc/self/fd/N. I think I have this case correct. > > What's the best way to fix this? Should I be checking nd->depth?
No, I think that's wrong, too. I think that will cause me to screw up symlinks to /proc/self/fd/3. What's the right way to tell that follow_link is happening on the very last pathname component?
Hmm. I wonder what happens, or even what should happen, if the file descriptor is a symlink opened with O_PATH | O_NOFOLLOW.
--Andy
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