[PATCH v2] firewire: cdev: check write quadlet request length to avoid buffer overflow
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From: Stefan Richter on 7 Jul 2010 06:00 Check that the data length of a write quadlet request actually is large enough for a quadlet. Otherwise, fw_fill_request could access the four bytes after the end of the outbound_transaction_event structure. Reported-by: Clemens Ladisch <clemens(a)ladisch.de> Since struct outbound_transaction_event *e is slab-allocated, such an access may hit unallocated memory only if sizeof(*e) == 256 or 512 or any other power of 2 above 2**2. In kernel 2.6.34, sizeof(*e) is > 128 and < 256 on 32bit architectures, and > 256 and < 512 on 64bit architectures. Thus the only problem is that a bogus write quadlet request with user-specified length of < 3 will put 1...4 random bytes into the packet payload; but this is the users's problem then, not the kernel's. Hence the corner case handling can be optimized by a !(sizeof(*e) & 255) check as a weaker form of a sizeof(*e) == 256 or 512 check. This is a constant expression and will cause the whole check to be omitted by the compiler's dead code elimination. Of course this relies on certain behavior of the slab allocator. Signed-off-by: Stefan Richter <stefanr(a)s5r6.in-berlin.de> --- drivers/firewire/core-cdev.c | 5 +++++ 1 file changed, 5 insertions(+) Index: b/drivers/firewire/core-cdev.c =================================================================== --- a/drivers/firewire/core-cdev.c +++ b/drivers/firewire/core-cdev.c @@ -564,6 +564,11 @@ static int init_request(struct client *c (request->length > 4096 || request->length > 512 << speed)) return -EIO; + /* Corner case: Access past the end of *e in fw_fill_request() */ + if (request->tcode == TCODE_WRITE_QUADLET_REQUEST && + request->length < 4 && (sizeof(*e) & 255) == 0) + return -EINVAL; + e = kmalloc(sizeof(*e) + request->length, GFP_KERNEL); if (e == NULL) return -ENOMEM; -- Stefan Richter -=====-==-=- -=== --=== http://arcgraph.de/sr/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |