Commit fc3dc674 authored by Jiri Slaby's avatar Jiri Slaby Committed by Jeff Layton

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:
 [<ffffffffad8f0868>] ? f_setown+0x1d8/0x200
 [<ffffffffad8f19a9>] ? SyS_fcntl+0x999/0xf30
 [<ffffffffaed1fb00>] ? 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:

        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: default avatarJiri Slaby <>
Cc: Jeff Layton <>
Cc: "J. Bruce Fields" <>
Cc: Alexander Viro <>
Signed-off-by: default avatarJeff Layton <>
parent 393cc3f5
......@@ -116,6 +116,10 @@ int f_setown(struct file *filp, unsigned long arg, int force)
int who = arg;
if (who < 0) {
/* avoid overflow below */
if (who == INT_MIN)
return -EINVAL;
who = -who;
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