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proc: only require mm_struct for writing 

Commit 591a22c14d ("proc: Track /proc/$pid/attr/ opener mm_struct") we
started using __mem_open() to track the mm_struct at open-time, so that
we could then check it for writes.

But that also ended up making the permission checks at open time much
stricter - and not just for writes, but for reads too.  And that in turn
caused a regression for at least Fedora 29, where NIC interfaces fail to
start when using NetworkManager.

Since only the write side wanted the mm_struct test, ignore any failures
by __mem_open() at open time, leaving reads unaffected.  The write()
time verification of the mm_struct pointer will then catch the failure
case because a NULL pointer will not match a valid 'current->mm'.

Link: https://lore.kernel.org/netdev/YMjTlp2FSJYvoyFa@unreal/
Fixes: 591a22c14d ("proc: Track /proc/$pid/attr/ opener mm_struct")
Reported-and-tested-by: Leon Romanovsky <leon@kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Cc: Christian Brauner <christian.brauner@ubuntu.com>
Cc: Andrea Righi <andrea.righi@canonical.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Linus Torvalds 2021-06-15 09:26:19 -07:00
parent a33d62662d
commit 94f0b2d4a1
1 changed files with 3 additions and 1 deletions
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4
fs/proc/base.c
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@ -2676,7 +2676,9 @@ out:
#ifdef CONFIG_SECURITY
static int proc_pid_attr_open(struct inode *inode, struct file *file)
{
return __mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
file->private_data = NULL;
__mem_open(inode, file, PTRACE_MODE_READ_FSCREDS);
return 0;
}
static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,