linux-kernel - [PATCH] prctl: move PR_GET_AUXV out of PR_MCE

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Date:   Sun,  9 Jul 2023 01:33:44 +0200
From:   Miguel Ojeda <ojeda@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Josh Triplett <josh@...htriplett.org>,
        linux-kernel@...r.kernel.org, Miguel Ojeda <ojeda@...nel.org>,
        stable@...r.kernel.org
Subject: [PATCH] prctl: move PR_GET_AUXV out of PR_MCE_KILL

Somehow PR_GET_AUXV got added into PR_MCE_KILL's switch when
the patch was applied [1].

Thus move it out of the switch, to the place the patch added it.

In the recently released v6.4 kernel some user could, in
principle, be already using this feature by mapping the right
page and passing the PR_GET_AUXV constant as a pointer:

    prctl(PR_MCE_KILL, PR_GET_AUXV, ...)

So this does change the behavior for users. We could keep the bug
since the other subcases in PR_MCE_KILL (PR_MCE_KILL_CLEAR and
PR_MCE_KILL_SET) do not overlap.

However, v6.4 may be recent enough (2 weeks old) that moving
the lines (rather than just adding a new case) does not break
anybody? Moreover, the documentation in man-pages was just
committed today [2].

Fixes: ddc65971bb67 ("prctl: add PR_GET_AUXV to copy auxv to userspace")
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/all/d81864a7f7f43bca6afa2a09fc2e850e4050ab42.1680611394.git.josh@joshtriplett.org/ [1]
Link: https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/commit/?id=8cf0c06bfd3c2b219b044d4151c96f0da50af9ad [2]
Signed-off-by: Miguel Ojeda <ojeda@...nel.org>
---
 kernel/sys.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/sys.c b/kernel/sys.c
index 339fee3eff6a..a36a27ebac33 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -2529,11 +2529,6 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 			else
 				return -EINVAL;
 			break;
-	case PR_GET_AUXV:
-		if (arg4 || arg5)
-			return -EINVAL;
-		error = prctl_get_auxv((void __user *)arg2, arg3);
-		break;
 		default:
 			return -EINVAL;
 		}
@@ -2688,6 +2683,11 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3,
 	case PR_SET_VMA:
 		error = prctl_set_vma(arg2, arg3, arg4, arg5);
 		break;
+	case PR_GET_AUXV:
+		if (arg4 || arg5)
+			return -EINVAL;
+		error = prctl_get_auxv((void __user *)arg2, arg3);
+		break;
 #ifdef CONFIG_KSM
 	case PR_SET_MEMORY_MERGE:
 		if (arg3 || arg4 || arg5)

base-commit: 6995e2de6891c724bfeb2db33d7b87775f913ad1
-- 
2.41.0