From: Davide Libenzi Davi fixed a missing cast in the __put_user(), that was making timerfd return a single byte instead of the full value. Talking with Michael about the timerfd man page, we think it'd be better to use a u64 for the returned value, to align it with the eventfd implementation. This is an ABI change. The timerfd code is new in 2.6.22 and if we merge this into 2.6.23 then we should also merge it into 2.6.22.x. That will leave a few early 2.6.22 kernels out in the wild which might misbehave when a future timerfd-enabled glibc is run on them. mtk says: The difference would be that read() will only return 4 bytes, while the application will expect 8. If the application is checking the size of returned value, as it should, then it will be able to detect the problem (it could even be sophisticated enough to know that if this is a 4-byte return, then it is running on an old 2.6.22 kernel). If the application is not checking the return from read(), then its 8-byte buffer will not be filled -- the contents of the last 4 bytes will be undefined, so the u64 value as a whole will be junk. When I wrote up that description above, I forgot a crucial detail. The above description described the difference between the new behavior implemented by the patch, and the current (i.e., 2.6.22) *intended* behavior. However, as I originally remarked to Davide, the 2.6.22 read() behavior is broken: it should return 4 bytes on a read(), but as originally implemented, only the least significant byte contained valid information. (In other words, the top 3 bytes of overrun information were simply being discarded.) So the patch both fixes a bug in the originally intended behavior, and changes the intended behavior (to return 8 bytes from a read() instead of 4). Signed-off-by: Davide Libenzi Cc: Michael Kerrisk Cc: Davi Arnaut Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman --- fs/timerfd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) --- a/fs/timerfd.c +++ b/fs/timerfd.c @@ -95,7 +95,7 @@ static ssize_t timerfd_read(struct file { struct timerfd_ctx *ctx = file->private_data; ssize_t res; - u32 ticks = 0; + u64 ticks = 0; DECLARE_WAITQUEUE(wait, current); if (count < sizeof(ticks)) @@ -130,7 +130,7 @@ static ssize_t timerfd_read(struct file * callback to avoid DoS attacks specifying a very * short timer period. */ - ticks = (u32) + ticks = (u64) hrtimer_forward(&ctx->tmr, hrtimer_cb_get_time(&ctx->tmr), ctx->tintv); @@ -140,7 +140,7 @@ static ssize_t timerfd_read(struct file } spin_unlock_irq(&ctx->wqh.lock); if (ticks) - res = put_user(ticks, buf) ? -EFAULT: sizeof(ticks); + res = put_user(ticks, (u64 __user *) buf) ? -EFAULT: sizeof(ticks); return res; } -- - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/