On 08/17/2016 07:39 PM, Jeff Layton wrote:
On Wed, 2016-08-17 at 19:34 +0200, Florian Weimer wrote:
On 08/17/2016 04:47 PM, Jeff Layton wrote:
The Linux kernel expects a flock64 structure whenever you use OFD locks
with fcntl64. Unfortunately, you can currently build a 32-bit program
that passes in a struct flock when it calls fcntl64.
Only define the F_OFD_* constants when __USE_FILE_OFFSET64 is also
defined, so that the build fails in this situation rather than
producing a broken binary.
Doesn't this affect legacy POSIX-style locks as well, under very similar
circumstances?
No. The kernel will decide which type of struct it is based on whether
userland passes in F_SETLK or F_SETLK64.
Let me see if I can sort this out. Is the situation like this?
_FILE_OFFSET_… …BITS == 32 …BITS == 64
struct … flock flock64 flock flock64
fcntl (F_SETLK) ok BAD ok BAD
fcntl (F_SETLK64) BAD ok ok ok
fcntl (F_OFD_SETLK) BAD ok¹ ok ok
¹ is broken by your patch, right?
Looking at the definition of struct flock and struct flock64, the risk
is that application silently succeed in locking the wrong thing when
using struct flock64 with a 32-it interface.
Thanks,
Florian
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