diff options
author | Laurent Vivier <lvivier@redhat.com> | 2019-10-14 13:46:32 +0200 |
---|---|---|
committer | Herbert Xu <herbert@gondor.apana.org.au> | 2019-10-23 19:47:00 +1100 |
commit | 28443671a468489fb147b31687b2157b6ba59c4a (patch) | |
tree | e9fe658a20ac17216e716945ef1ea817aa99484e /drivers/char/hw_random | |
parent | 4ba802980cadb2c6a30e277f4d0a1a64df7fdb1c (diff) |
hwrng: core - Fix use-after-free warning in hwrng_register()
Commit daae28debcb0 has moved add_early_randomness() out of the
rng_mutex and tries to protect the reference of the new rng device
by incrementing the reference counter.
But in hwrng_register(), the function can be called with a new device
that is not set as the current_rng device and the reference has not been
initialized. This patch fixes the problem by not using the reference
counter when the device is not the current one: the reference counter
is only meaningful in the case of the current rng device and a device
is not used if it is not the current one (except in hwrng_register())
The problem has been reported by Marek Szyprowski on ARM 32bit
Exynos5420-based Chromebook Peach-Pit board:
WARNING: CPU: 3 PID: 1 at lib/refcount.c:156 hwrng_register+0x13c/0x1b4
refcount_t: increment on 0; use-after-free.
Modules linked in:
CPU: 3 PID: 1 Comm: swapper/0 Not tainted 5.4.0-rc1-00061-gdaae28debcb0
Hardware name: SAMSUNG EXYNOS (Flattened Device Tree)
[<c01124c8>] (unwind_backtrace) from [<c010dfb8>] (show_stack+0x10/0x14)
[<c010dfb8>] (show_stack) from [<c0ae86d8>] (dump_stack+0xa8/0xd4)
[<c0ae86d8>] (dump_stack) from [<c0127428>] (__warn+0xf4/0x10c)
[<c0127428>] (__warn) from [<c01274b4>] (warn_slowpath_fmt+0x74/0xb8)
[<c01274b4>] (warn_slowpath_fmt) from [<c054729c>] (hwrng_register+0x13c/0x1b4)
[<c054729c>] (hwrng_register) from [<c0547e54>] (tpm_chip_register+0xc4/0x274)
...
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Fixes: daae28debcb0 ("hwrng: core - move add_early_randomness() out of rng_mutex")
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Diffstat (limited to 'drivers/char/hw_random')
-rw-r--r-- | drivers/char/hw_random/core.c | 33 |
1 files changed, 16 insertions, 17 deletions
diff --git a/drivers/char/hw_random/core.c b/drivers/char/hw_random/core.c index 29f50c045c92..d85c6e18a2d2 100644 --- a/drivers/char/hw_random/core.c +++ b/drivers/char/hw_random/core.c @@ -471,17 +471,15 @@ static void start_khwrngd(void) int hwrng_register(struct hwrng *rng) { int err = -EINVAL; - struct hwrng *old_rng, *new_rng, *tmp; + struct hwrng *tmp; struct list_head *rng_list_ptr; + bool is_new_current = false; if (!rng->name || (!rng->data_read && !rng->read)) goto out; mutex_lock(&rng_mutex); - old_rng = current_rng; - new_rng = NULL; - /* Must not register two RNGs with the same name. */ err = -EEXIST; list_for_each_entry(tmp, &rng_list, list) { @@ -500,9 +498,8 @@ int hwrng_register(struct hwrng *rng) } list_add_tail(&rng->list, rng_list_ptr); - err = 0; - if (!old_rng || - (!cur_rng_set_by_user && rng->quality > old_rng->quality)) { + if (!current_rng || + (!cur_rng_set_by_user && rng->quality > current_rng->quality)) { /* * Set new rng as current as the new rng source * provides better entropy quality and was not @@ -511,15 +508,14 @@ int hwrng_register(struct hwrng *rng) err = set_current_rng(rng); if (err) goto out_unlock; + /* to use current_rng in add_early_randomness() we need + * to take a ref + */ + is_new_current = true; + kref_get(&rng->ref); } - - new_rng = rng; - kref_get(&new_rng->ref); -out_unlock: mutex_unlock(&rng_mutex); - - if (new_rng) { - if (new_rng != old_rng || !rng->init) { + if (is_new_current || !rng->init) { /* * Use a new device's input to add some randomness to * the system. If this rng device isn't going to be @@ -527,10 +523,13 @@ out_unlock: * called yet by set_current_rng(); so only use the * randomness from devices that don't need an init callback */ - add_early_randomness(new_rng); - } - put_rng(new_rng); + add_early_randomness(rng); } + if (is_new_current) + put_rng(rng); + return 0; +out_unlock: + mutex_unlock(&rng_mutex); out: return err; } |