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Subject[PATCH 4.12 50/52] idr: remove WARN_ON_ONCE() when trying to replace negative ID
4.12-stable review patch.  If anyone has any objections, please let me know.


From: Eric Biggers <>

commit a47f68d6a944113bdc8097db6f933c2e17c27bf9 upstream.

IDR only supports non-negative IDs. There used to be a 'WARN_ON_ONCE(id <
0)' in idr_replace(), but it was intentionally removed by commit
2e1c9b286765 ("idr: remove WARN_ON_ONCE() on negative IDs").

Then it was added back by commit 0a835c4f090a ("Reimplement IDR and IDA
using the radix tree"). However it seems that adding it back was a
mistake, given that some users such as drm_gem_handle_delete()
(DRM_IOCTL_GEM_CLOSE) pass in a value from userspace to idr_replace(),
allowing the WARN_ON_ONCE to be triggered. drm_gem_handle_delete()
actually just wants idr_replace() to return an error code if the ID is
not allocated, including in the case where the ID is invalid (negative).

So once again remove the bogus WARN_ON_ONCE().

This bug was found by syzkaller, which encountered the following

WARNING: CPU: 3 PID: 3008 at lib/idr.c:157 idr_replace+0x1d8/0x240 lib/idr.c:157
Kernel panic - not syncing: panic_on_warn set ...

CPU: 3 PID: 3008 Comm: syzkaller218828 Not tainted 4.13.0-rc4-next-20170811 #2
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
Call Trace:
fixup_bug+0x40/0x90 arch/x86/kernel/traps.c:190
do_trap_no_signal arch/x86/kernel/traps.c:224 [inline]
do_trap+0x260/0x390 arch/x86/kernel/traps.c:273
do_error_trap+0x120/0x390 arch/x86/kernel/traps.c:310
do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:323
invalid_op+0x1e/0x30 arch/x86/entry/entry_64.S:930
RIP: 0010:idr_replace+0x1d8/0x240 lib/idr.c:157
RSP: 0018:ffff8800394bf9f8 EFLAGS: 00010297
RAX: ffff88003c6c60c0 RBX: 1ffff10007297f43 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff8800394bfa78
RBP: ffff8800394bfae0 R08: ffffffff82856487 R09: 0000000000000000
R10: ffff8800394bf9a8 R11: ffff88006c8bae28 R12: ffffffffffffffff
R13: ffff8800394bfab8 R14: dffffc0000000000 R15: ffff8800394bfbc8
drm_gem_handle_delete+0x33/0xa0 drivers/gpu/drm/drm_gem.c:297
drm_gem_close_ioctl+0xa1/0xe0 drivers/gpu/drm/drm_gem.c:671
drm_ioctl_kernel+0x1e7/0x2e0 drivers/gpu/drm/drm_ioctl.c:729
drm_ioctl+0x72e/0xa50 drivers/gpu/drm/drm_ioctl.c:825
vfs_ioctl fs/ioctl.c:45 [inline]
do_vfs_ioctl+0x1b1/0x1520 fs/ioctl.c:685
SYSC_ioctl fs/ioctl.c:700 [inline]
SyS_ioctl+0x8f/0xc0 fs/ioctl.c:691

Here is a C reproducer:

#include <fcntl.h>
#include <stddef.h>
#include <stdint.h>
#include <sys/ioctl.h>
#include <drm/drm.h>

int main(void)
int cardfd = open("/dev/dri/card0", O_RDONLY);

ioctl(cardfd, DRM_IOCTL_GEM_CLOSE,
&(struct drm_gem_close) { .handle = -1 } );

Fixes: 0a835c4f090a ("Reimplement IDR and IDA using the radix tree")
Signed-off-by: Eric Biggers <>
Acked-by: Tejun Heo <>
Cc: Dmitry Vyukov <>
Cc: Matthew Wilcox <>
Signed-off-by: Andrew Morton <>
Signed-off-by: Linus Torvalds <>
Signed-off-by: Greg Kroah-Hartman <>

lib/idr.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/lib/idr.c
+++ b/lib/idr.c
@@ -154,7 +154,7 @@ void *idr_replace(struct idr *idr, void
void __rcu **slot = NULL;
void *entry;

- if (WARN_ON_ONCE(id < 0))
+ if (id < 0)
return ERR_PTR(-EINVAL);
if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
return ERR_PTR(-EINVAL);

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