From fc3dc67471461c0efcb1ed22fb7595121d65fad9 Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Tue, 13 Jun 2017 13:35:51 +0200 Subject: [PATCH] fs/fcntl: f_setown, avoid undefined behaviour fcntl(0, F_SETOWN, 0x80000000) triggers: UBSAN: Undefined behaviour in fs/fcntl.c:118:7 negation of -2147483648 cannot be represented in type 'int': CPU: 1 PID: 18261 Comm: syz-executor Not tainted 4.8.1-0-syzkaller #1 ... Call Trace: ... [] ? f_setown+0x1d8/0x200 [] ? SyS_fcntl+0x999/0xf30 [] ? entry_SYSCALL_64_fastpath+0x23/0xc1 Fix that by checking the arg parameter properly (against INT_MAX) before "who = -who". And return immediatelly with -EINVAL in case it is wrong. Note that according to POSIX we can return EINVAL: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fcntl.html [EINVAL] The cmd argument is F_SETOWN and the value of the argument is not valid as a process or process group identifier. [v2] returns an error, v1 used to fail silently [v3] implement proper check for the bad value INT_MIN Signed-off-by: Jiri Slaby Cc: Jeff Layton Cc: "J. Bruce Fields" Cc: Alexander Viro Cc: linux-fsdevel@vger.kernel.org Signed-off-by: Jeff Layton --- fs/fcntl.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/fs/fcntl.c b/fs/fcntl.c index 313eba8..693322e 100644 --- a/fs/fcntl.c +++ b/fs/fcntl.c @@ -116,6 +116,10 @@ int f_setown(struct file *filp, unsigned long arg, int force) int who = arg; type = PIDTYPE_PID; if (who < 0) { + /* avoid overflow below */ + if (who == INT_MIN) + return -EINVAL; + type = PIDTYPE_PGID; who = -who; } -- 2.7.4