Since commit 5d47ec02c37ea632398cb251c884e3a488dff794
("firmware: Correct handling of fw_state_wait() return value")
fw_load_abort(fw_priv) could be called twice and lead us to a
kernel crash. This happens only when the firmware fallback mechanism
(regular or custom) is used. The fallback mechanism exposes a sysfs
interface for userspace to upload a file and notify the kernel when
the file is loaded and ready, or to cancel an upload by echo'ing -1
into on the loading file:
echo -n "-1" > /sys/$DEVPATH/loading
This will call fw_load_abort(). Some distributions actually have
a udev rule in place to *always* immediately cancel all firmware
fallback mechanism requests (Debian, OpenSUSE), they have:
$ cat /lib/udev/rules.d/50-firmware.rules
# stub for immediately telling the kernel that userspace firmware loading
# failed; necessary to avoid long timeouts with CONFIG_FW_LOADER_USER_HELPER=y
SUBSYSTEM=="firmware", ACTION=="add", ATTR{loading}="-1
This was done since udev removed the firmware fallback mechanism a while ago
and a long standing misunderstood issues with the timeout (but now corrected).
Distributions with this udev rule would run into this crash only if the
fallback mechanism is used. Since most distributions disable by default
using the fallback mechanism (CONFIG_FW_LOADER_USER_HELPER_FALLBACK), this
would typicaly mean only 2 drivers which *require* the fallback mechanism
could typically incur a crash: drivers/firmware/dell_rbu.c and the
drivers/leds/leds-lp55xx-common.c driver.
Distributions enabling CONFIG_FW_LOADER_USER_HELPER_FALLBACK are clearly
more exposed as every file not found through a firmware request will
use the fallback mechanism.
The crash happens because after commit 5b029624948d ("firmware: do not
use fw_lock for fw_state protection") and subsequent fix commit
5d47ec02c37ea6 ("firmware: Correct handling of fw_state_wait() return
value") a race can happen between this cancelation and the firmware
fw_state_wait_timeout() being woken up after a state change with which
fw_load_abort() as that calls swake_up(). Upon error fw_state_wait_timeout()
will also again call fw_load_abort() and trigger a null reference.
At first glance we could just fix this with a !buf check on
fw_load_abort() before accessing buf->fw_st, however there is
a logical issue in having a state machine used for the fallback
mechanism and preventing access from it once we abort as its inside
the buf (buf->fw_st).
The firmware_class.c code is setting the buf to NULL to annotate an
abort has occurred. Replace this mechanism by simply using the state check
instead. All the other code in place already uses similar checks
for aborting as well so no further changes are needed.
An oops can be reproduced with the new fw_fallback.sh fallback
mechanism cancellation test. Either cancelling the fallback mechanism
or the custom fallback mechanism triggers a crash.
mcgrof@piggy ~/linux-next/tools/testing/selftests/firmware
(git::20170111-fw-fixes)$ sudo ./fw_fallback.sh
./fw_fallback.sh: timeout works
./fw_fallback.sh: firmware comparison works
./fw_fallback.sh: fallback mechanism works
[ this then sits here when it is trying the cancellation test ]
Kernel log:
[ 36.750521] test_firmware: loading 'nope-test-firmware.bin'
[ 36.751144] misc test_firmware: Direct firmware load for nope-test-firmware.bin failed with error -2
[ 36.752034] misc test_firmware: Falling back to user helper
[ 36.853324] BUG: unable to handle kernel NULL pointer dereference at 0000000000000038
[ 36.854221] IP: _request_firmware+0xa27/0xad0
[ 36.854671] PGD 0
[ 36.854672]
[ 36.855081] Oops: 0000 [#1] SMP
[ 36.855433] Modules linked in: test_firmware(E) ... etc ...
[ 36.857802] CPU: 1 PID: 1396 Comm: fw_fallback.sh Tainted: G W E 4.10.0-rc3-next-20170111+ #30
[ 36.857802] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.10.1-0-g8891697-prebuilt.qemu-project.org 04/01/2014
[ 36.857802] task: ffff9740b27f4340 task.stack: ffffbb15c0bc8000
[ 36.857802] RIP: 0010:_request_firmware+0xa27/0xad0
[ 36.857802] RSP: 0018:ffffbb15c0bcbd10 EFLAGS: 00010246
[ 36.857802] RAX: 00000000fffffffe RBX: ffff9740afe5aa80 RCX: 0000000000000000
[ 36.857802] RDX: ffff9740b27f4340 RSI: 0000000000000283 RDI: 0000000000000000
[ 36.857802] RBP: ffffbb15c0bcbd90 R08: ffffbb15c0bcbcd8 R09: 0000000000000000
[ 36.857802] R10: 0000000894a0d4b1 R11: 000000000000008c R12: ffffffffc0312480
[ 36.857802] R13: 0000000000000005 R14: ffff9740b1c32400 R15: 00000000000003e8
[ 36.857802] FS: 00007f8604422700(0000) GS:ffff9740bfc80000(0000) knlGS:0000000000000000
[ 36.857802] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 36.857802] CR2: 0000000000000038 CR3: 000000012164c000 CR4: 00000000000006e0
[ 36.857802] Call Trace:
[ 36.857802] request_firmware+0x37/0x50
[ 36.857802] trigger_request_store+0x79/0xd0 [test_firmware]
[ 36.857802] dev_attr_store+0x18/0x30
[ 36.857802] sysfs_kf_write+0x37/0x40
[ 36.857802] kernfs_fop_write+0x110/0x1a0
[ 36.857802] __vfs_write+0x37/0x160
[ 36.857802] ? _cond_resched+0x1a/0x50
[ 36.857802] vfs_write+0xb5/0x1a0
[ 36.857802] SyS_write+0x55/0xc0
[ 36.857802] ? trace_do_page_fault+0x37/0xd0
[ 36.857802] entry_SYSCALL_64_fastpath+0x1e/0xad
[ 36.857802] RIP: 0033:0x7f8603f49620
[ 36.857802] RSP: 002b:00007fff6287b788 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
[ 36.857802] RAX: ffffffffffffffda RBX: 000055c307b110a0 RCX: 00007f8603f49620
[ 36.857802] RDX: 0000000000000016 RSI: 000055c3084d8a90 RDI: 0000000000000001
[ 36.857802] RBP: 0000000000000016 R08: 000000000000c0ff R09: 000055c3084d6336
[ 36.857802] R10: 000055c307b108b0 R11: 0000000000000246 R12: 000055c307b13c80
[ 36.857802] R13: 000055c3084d6320 R14: 0000000000000000 R15: 00007fff6287b950
[ 36.857802] Code: 9f 64 84 e8 9c 61 fe ff b8 f4 ff ff ff e9 6b f9 ff
ff 48 c7 c7 40 6b 8d 84 89 45 a8 e8 43 84 18 00 49 8b be 00 03 00 00 8b
45 a8 <83> 7f 38 02 74 08 e8 6e ec ff ff 8b 45 a8 49 c7 86 00 03 00 00
[ 36.857802] RIP: _request_firmware+0xa27/0xad0 RSP: ffffbb15c0bcbd10
[ 36.857802] CR2: 0000000000000038
[ 36.872685] ---[ end trace 6d94ac339c133e6f ]---
In above case the call hierarchy that causes the crash looks as follows:
lib/test_firmware.c request_firmware()
-> fw_load_from_user_helper()
-> _request_firmware_load()
-> call fw_state_wait_timeout()
Some time later firmware_loading_store() scans a control value of "-1"
-> switch(loading) case -1: will call
-> fw_load_abort(fw_priv) which calls
-> __fw_load_abort(fw_priv->buf)
-> and set fw_priv->buf = NULL;
Upon being woken up via swake_up(), back in _request_firmware_load()
fw_state_wait_timeout() returns -ENOENT
-> since mentioned commit
-> fw_load_abort(fw_priv) is called a second time
-> and this time it would call:
-> __fw_load_abort(NULL /* fw_priv->buf */)
-> and we get: NULL->fw_st.status
Fixes: 5d47ec02c37e ("firmware: Correct handling of fw_state_wait() return value")
Reported-and-Tested-by: Jakub Kicinski <jakub.kicinski@xxxxxxxxxxxxx>
Reported-and-Tested-by: Patrick Bruenn <p.bruenn@xxxxxxxxxxxx>
Reported-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
CC: <stable@xxxxxxxxxxxxxxx> [3.10+]
Signed-off-by: Luis R. Rodriguez <mcgrof@xxxxxxxxxx>
---
drivers/base/firmware_class.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
diff --git a/drivers/base/firmware_class.c b/drivers/base/firmware_class.c
index 4497d263209f..ac350c518e0c 100644
--- a/drivers/base/firmware_class.c
+++ b/drivers/base/firmware_class.c
@@ -558,9 +558,6 @@ static void fw_load_abort(struct firmware_priv *fw_priv)
struct firmware_buf *buf = fw_priv->buf;
__fw_load_abort(buf);
-
- /* avoid user action after loading abort */
- fw_priv->buf = NULL;
}
static LIST_HEAD(pending_fw_head);
@@ -713,7 +710,7 @@ static ssize_t firmware_loading_store(struct device *dev,
mutex_lock(&fw_lock);
fw_buf = fw_priv->buf;
- if (!fw_buf)
+ if (fw_state_is_aborted(&fw_buf->fw_st))
goto out;
switch (loading) {
--
2.11.0
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