[Qemu-devel] [PATCH for-2.7] linux-user: Fix llseek with high bit of offset_low set

[Peter Maydell <peter.maydell@linaro.org>]

The llseek syscall takes two 32-bit arguments, offset_high
and offset_low, which must be combined to form a single
64-bit offset. Unfortunately we were combining them with
   (uint64_t)arg2 << 32) | arg3
and arg3 is a signed type; this meant that when promoting
arg3 to a 64-bit type it would be sign-extended. The effect
was that if the offset happened to have bit 31 set then
this bit would get sign-extended into all of bits 63..32.
Explicitly cast arg3 to abi_ulong to avoid the erroneous
sign extension.

Reported-by: Chanho Park <parkch98@gmail.com>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Long-standing bug and we're quite close to 2.7 but the
fix is trivial so if somebody would like to review it
I think we could put it in...

 linux-user/syscall.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index ebdb753..b4e21d3 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -9406,7 +9406,7 @@ abi_long do_syscall(void *cpu_env, int num, abi_long arg1,
         {
             int64_t res;
 #if !defined(__NR_llseek)
-            res = lseek(arg1, ((uint64_t)arg2 << 32) | arg3, arg5);
+            res = lseek(arg1, ((uint64_t)arg2 << 32) | (abi_ulong)arg3, arg5);
             if (res == -1) {
                 ret = get_errno(res);
             } else {
-- 
2.7.4