[PATCH 5.4 223/367] procfs: block chmod on /proc/thread-self/comm

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5.4-stable review patch.  If anyone has any objections, please let me know.


From: Aleksa Sarai <cyphar@xxxxxxxxxx>

commit ccf61486fe1e1a48e18c638d1813cda77b3c0737 upstream.

Due to an oversight in commit 1b3044e39a89 ("procfs: fix pthread
cross-thread naming if !PR_DUMPABLE") in switching from REG to NOD,
chmod operations on /proc/thread-self/comm were no longer blocked as
they are on almost all other procfs files.

A very similar situation with /proc/self/environ was used to as a root
exploit a long time ago, but procfs has SB_I_NOEXEC so this is simply a
correctness issue.

Ref: https://lwn.net/Articles/191954/
Ref: 6d76fa58b050 ("Don't allow chmod() on the /proc/<pid>/ files")
Fixes: 1b3044e39a89 ("procfs: fix pthread cross-thread naming if !PR_DUMPABLE")
Cc: stable@xxxxxxxxxxxxxxx # v4.7+
Signed-off-by: Aleksa Sarai <cyphar@xxxxxxxxxx>
Message-Id: <20230713141001.27046-1-cyphar@xxxxxxxxxx>
Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
 fs/proc/base.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -3412,7 +3412,8 @@ static int proc_tid_comm_permission(stru
 static const struct inode_operations proc_tid_comm_inode_operations = {
-		.permission = proc_tid_comm_permission,
+		.setattr	= proc_setattr,
+		.permission	= proc_tid_comm_permission,

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