From: Eric Biggers ebiggers@google.com

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:

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: __dump_stack lib/dump_stack.c:16 [inline] dump_stack+0x194/0x257 lib/dump_stack.c:52 panic+0x1e4/0x417 kernel/panic.c:180 __warn+0x1c4/0x1d9 kernel/panic.c:541 report_bug+0x211/0x2d0 lib/bug.c:183 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 entry_SYSCALL_64_fastpath+0x1f/0xbe

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") Cc: Andrew Morton akpm@linux-foundation.org Cc: Chris Wilson chris@chris-wilson.co.uk Cc: Dmitry Vyukov dvyukov@google.com Cc: Matthew Wilcox mawilcox@microsoft.com Cc: Tejun Heo tj@kernel.org Cc: dri-devel@lists.freedesktop.org Cc: stable@vger.kernel.org [v4.11+] Signed-off-by: Eric Biggers ebiggers@google.com --- lib/idr.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/lib/idr.c b/lib/idr.c index 082778cf883e..f9adf4805fd7 100644 --- a/lib/idr.c +++ b/lib/idr.c @@ -151,7 +151,7 @@ EXPORT_SYMBOL(idr_get_next_ext); */ void *idr_replace(struct idr *idr, void *ptr, int id) { - if (WARN_ON_ONCE(id < 0)) + if (id < 0) return ERR_PTR(-EINVAL);

return idr_replace_ext(idr, ptr, id);