Messages in this thread Patch in this message | | | From | Ahmad Fatoum <> | Subject | [PATCH RFC] proc: Don't retain negative dentries | Date | Mon, 8 Oct 2018 18:50:10 +0200 |
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The referenced commit 1da4d377f94 ("proc: revalidate misc dentries") caused following userspace code to access a stale /proc/net/dev after the network namespace was changed:
system("ip netns add testns");
printf("default:\n"); { int devinfd = open("/proc/net/dev", O_RDONLY); sendfile(STDOUT_FILENO, devinfd, NULL, 4096); close(devinfd); }
printf("testns:\n"); { int ns_fd = open("/var/run/netns/testns", O_RDONLY); setns(ns_fd, 0);
int devinfd = open("/proc/net/dev", O_RDONLY); sendfile(STDOUT_FILENO, devinfd, NULL, 4096); close(devinfd);
close(ns_fd); }
Despite switching the network namespace, the read access from the newly opened file gave back what the very first read in the default network namespace returned.
This doesn't occur if /proc/net/dev is opened within a new process, which might explain why this wasn't noticed previously.
As I don't see a reason why one would keep negative dentries for procfs at all, amend the code not to do this anymore.
Fixes: 1da4d377f94 ("proc: Don't retain negative dentries") Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de> ---
Notes: Alexey, could you check this doesn't lead to a regression concerning the bug you fixed?
fs/proc/generic.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/fs/proc/generic.c b/fs/proc/generic.c index 8ae109429a88..412b3c52d5d5 100644 --- a/fs/proc/generic.c +++ b/fs/proc/generic.c @@ -231,7 +231,7 @@ static int proc_misc_d_revalidate(struct dentry *dentry, unsigned int flags) static int proc_misc_d_delete(const struct dentry *dentry) { - return atomic_read(&PDE(d_inode(dentry))->in_use) < 0; + return 1; // Don't retain negative dentries } static const struct dentry_operations proc_misc_dentry_ops = { -- 2.19.0
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