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coredump: fix PIDFD_INFO_COREDUMP ioctl check

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In Commit 1d8db6fd69 ("pidfs,
coredump: add PIDFD_INFO_COREDUMP"), the following code was added:

    if (mask & PIDFD_INFO_COREDUMP) {
        kinfo.mask |= PIDFD_INFO_COREDUMP;
        kinfo.coredump_mask = READ_ONCE(pidfs_i(inode)->__pei.coredump_mask);
    }
    [...]
    if (!(kinfo.mask & PIDFD_INFO_COREDUMP)) {
        task_lock(task);
        if (task->mm)
            kinfo.coredump_mask = pidfs_coredump_mask(task->mm->flags);
        task_unlock(task);
    }

The second bit in particular looks off to me - the condition in essence
checks whether PIDFD_INFO_COREDUMP was **not** requested, and if so
fetches the coredump_mask in kinfo, since it's checking !(kinfo.mask &
PIDFD_INFO_COREDUMP), which is unconditionally set in the earlier hunk.

I'm tempted to assume the idea in the second hunk was to calculate the
coredump mask if one was requested but fetched in the first hunk, in
which case the check should be
    if ((kinfo.mask & PIDFD_INFO_COREDUMP) && !(kinfo.coredump_mask))
which might be more legibly written as
    if ((mask & PIDFD_INFO_COREDUMP) && !(kinfo.coredump_mask))

This could also instead be achieved by changing the first hunk to be:

    if (mask & PIDFD_INFO_COREDUMP) {
	kinfo.coredump_mask = READ_ONCE(pidfs_i(inode)->__pei.coredump_mask);
	if (kinfo.coredump_mask)
	    kinfo.mask |= PIDFD_INFO_COREDUMP;
    }

and the second hunk to:

    if ((mask & PIDFD_INFO_COREDUMP) && !(kinfo.mask & PIDFD_INFO_COREDUMP)) {
	task_lock(task);
        if (task->mm) {
	    kinfo.coredump_mask = pidfs_coredump_mask(task->mm->flags);
            kinfo.mask |= PIDFD_INFO_COREDUMP;
        }
        task_unlock(task);
    }

However, when looking at this, the supposition that the second hunk
means to cover cases where the coredump info was requested but the first
hunk failed to get it starts getting doubtful, so apologies if I'm
completely off-base.

This patch addresses the issue by fixing the check in the second hunk.

Signed-off-by: Laura Brehm <laurabrehm@hey.com>
Link: https://lore.kernel.org/20250703120244.96908-3-laurabrehm@hey.com
Cc: brauner@kernel.org
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>
This commit is contained in:
Laura Brehm
2025-07-03 14:02:44 +02:00
committed by Christian Brauner
parent d7b8f8e208
commit 830a9e37cf
1 changed files with 1 additions and 1 deletions
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2
fs/pidfs.c
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@@ -319,7 +319,7 @@ static long pidfd_info(struct file *file, unsigned int cmd, unsigned long arg)
if (!c)
return -ESRCH;
if (!(kinfo.mask & PIDFD_INFO_COREDUMP)) {
if ((kinfo.mask & PIDFD_INFO_COREDUMP) && !(kinfo.coredump_mask)) {
task_lock(task);
if (task->mm)
kinfo.coredump_mask = pidfs_coredump_mask(task->mm->flags);