linux-kernel - [PATCH 19/20] signalfd: Fix handling of ssi_ptr and ssi_int in signalfd

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Date:	Wed, 14 Oct 2015 21:59:29 +0100
From:	Amanieu d'Antras <amanieu@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	Oleg Nesterov <oleg@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, x86@...nel.org,
	Brian Gerst <brgerst@...il.com>,
	Amanieu d'Antras <amanieu@...il.com>
Subject: [PATCH 19/20] signalfd: Fix handling of ssi_ptr and ssi_int in signalfd_copyinfo

There are several issues here:
1) The value of ssi_ptr was incorrect for 32-bit processes. It was
   previously copied directly from si_ptr, which contains garbage
   on 32-bit processes, especially on big-endian architectures.

2) A SIGSYS would cause various fields to be filled with incorrect
   values. SIGSYS fields are not in signalfd_siginfo, and it should
   avoid filling in unrelated fields.

3) ssi_ptr and ssi_int should not be filled in for any unrecognized
   si_code, but only for those generated by sigqueue. The si_ptr
   and si_int fields in siginfo_t may not be initialized otherwise.

Signed-off-by: Amanieu d'Antras <amanieu@...il.com>
---
 fs/signalfd.c | 42 +++++++++++++++++++++++++++++++-----------
 1 file changed, 31 insertions(+), 11 deletions(-)

diff --git a/fs/signalfd.c b/fs/signalfd.c
index 270221f..4d59de9 100644
--- a/fs/signalfd.c
+++ b/fs/signalfd.c
@@ -80,22 +80,43 @@ static unsigned int signalfd_poll(struct file *file, poll_table *wait)
 static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
 			     siginfo_t const *kinfo)
 {
-	long err;
+	long err, ssi_ptr;
 
 	BUILD_BUG_ON(sizeof(struct signalfd_siginfo) != 128);
 
 	/*
+	 * ssi_ptr for a compat task should be sourced from si_int instead
+	 * of si_ptr since that is what copy_siginfo_from_user32 and
+	 * get_compat_sigevent use. 32-bit pointer values are sign-extended
+	 * to 64 bits when written to ssi_ptr, which matches the behavior of
+	 * 32-bit kernels.
+	 */
+	ssi_ptr = is_compat_task() ? kinfo->si_int : (long) kinfo->si_ptr;
+
+	/*
 	 * Unused members should be zero ...
 	 */
 	err = __clear_user(uinfo, sizeof(*uinfo));
 
 	/*
-	 * If you change siginfo_t structure, please be sure
-	 * this code is fixed accordingly.
+	 * If you change siginfo_t structure, please be sure that
+	 * all these functions are fixed accordingly:
+	 * copy_siginfo_to_user
+	 * copy_siginfo_to_user32
+	 * copy_siginfo_from_user32
+	 * signalfd_copyinfo
+	 * They should never copy any pad contained in the structure
+	 * to avoid security leaks, but must copy the generic
+	 * 3 ints plus the relevant union member.
 	 */
 	err |= __put_user(kinfo->si_signo, &uinfo->ssi_signo);
 	err |= __put_user(kinfo->si_errno, &uinfo->ssi_errno);
 	err |= __put_user((short) kinfo->si_code, &uinfo->ssi_code);
+	if (kinfo->si_code < 0) {
+		/* Write ssi_int and ssi_ptr for sigqueue()-generated signals */
+		err |= __put_user(ssi_ptr, &uinfo->ssi_ptr);
+		err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
+	}
 	switch (kinfo->si_code & __SI_MASK) {
 	case __SI_KILL:
 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
@@ -104,7 +125,7 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
 	case __SI_TIMER:
 		 err |= __put_user(kinfo->si_tid, &uinfo->ssi_tid);
 		 err |= __put_user(kinfo->si_overrun, &uinfo->ssi_overrun);
-		 err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
+		 err |= __put_user(ssi_ptr, &uinfo->ssi_ptr);
 		 err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 		break;
 	case __SI_POLL:
@@ -139,21 +160,20 @@ static int signalfd_copyinfo(struct signalfd_siginfo __user *uinfo,
 	case __SI_MESGQ: /* But this is */
 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
-		err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
+		err |= __put_user(ssi_ptr, &uinfo->ssi_ptr);
 		err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 		break;
+#ifdef __ARCH_SIGSYS
+	case __SI_SYS: /* SIGSYS fields are not in signalfd_siginfo */
+		break;
+#endif
 	default:
-		/*
-		 * This case catches also the signals queued by sigqueue().
-		 */
 		err |= __put_user(kinfo->si_pid, &uinfo->ssi_pid);
 		err |= __put_user(kinfo->si_uid, &uinfo->ssi_uid);
-		err |= __put_user((long) kinfo->si_ptr, &uinfo->ssi_ptr);
-		err |= __put_user(kinfo->si_int, &uinfo->ssi_int);
 		break;
 	}
 
-	return err ? -EFAULT: sizeof(*uinfo);
+	return err ? -EFAULT : sizeof(*uinfo);
 }
 
 static ssize_t signalfd_dequeue(struct signalfd_ctx *ctx, siginfo_t *info,
-- 
2.6.1

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