[Qemu-devel] [PATCH 4/6] mips: rlimit incorrectly converts values

[Wesley W. Terpstra]

Byte swap was applied in the wrong order with testing for
RLIM_INFINITY. On mips bigendian from an amd64 system this results in
infinity being misinterpretted as 2^31-1.

This is a serious bug because it causes setrlimit stack size to kill
all child processes. This means (for example) that 'make' can run no
children. The mechanism of failure:
1. parent sets stack size rlimit to 'infinity'
2. qemu screws this value up
3. child process fetches stack size as a large (but non-infinite) value
4. qemu tries to allocate stack before execution
5. stack allocation fails (too big) and child process dies

Signed-off-by: Wesley W. Terpstra <terps...@debian.org>
---

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index fed7a8f..0b0a3d0 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -919,18 +919,30 @@ static inline abi_long
host_to_target_rusage(abi_ulong target_addr,

 static inline rlim_t target_to_host_rlim(target_ulong target_rlim)
 {
-    if (target_rlim == TARGET_RLIM_INFINITY)
-        return RLIM_INFINITY;
+    target_ulong target_rlim_swap;
+    rlim_t result;
+
+    target_rlim_swap = tswapl(target_rlim);
+    if (target_rlim_swap == TARGET_RLIM_INFINITY || target_rlim_swap
!= (rlim_t)target_rlim_swap)
+        result = RLIM_INFINITY;
     else
-        return tswapl(target_rlim);
+        result = target_rlim_swap;
+
+    return result;
 }

 static inline target_ulong host_to_target_rlim(rlim_t rlim)
 {
+    target_ulong target_rlim_swap;
+    target_ulong result;
+
     if (rlim == RLIM_INFINITY || rlim != (target_long)rlim)
-        return TARGET_RLIM_INFINITY;
+        target_rlim_swap = TARGET_RLIM_INFINITY;
     else
-        return tswapl(rlim);
+        target_rlim_swap = rlim;
+    result = tswapl(target_rlim_swap);
+
+    return result;
 }

 static inline abi_long copy_from_user_timeval(struct timeval *tv,

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index fed7a8f..0b0a3d0 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -919,18 +919,30 @@ static inline abi_long host_to_target_rusage(abi_ulong target_addr,
 
 static inline rlim_t target_to_host_rlim(target_ulong target_rlim)
 {
-    if (target_rlim == TARGET_RLIM_INFINITY)
-        return RLIM_INFINITY;
+    target_ulong target_rlim_swap;
+    rlim_t result;
+    
+    target_rlim_swap = tswapl(target_rlim);
+    if (target_rlim_swap == TARGET_RLIM_INFINITY || target_rlim_swap != (rlim_t)target_rlim_swap)
+        result = RLIM_INFINITY;
     else
-        return tswapl(target_rlim);
+        result = target_rlim_swap;
+    
+    return result;
 }
 
 static inline target_ulong host_to_target_rlim(rlim_t rlim)
 {
+    target_ulong target_rlim_swap;
+    target_ulong result;
+    
     if (rlim == RLIM_INFINITY || rlim != (target_long)rlim)
-        return TARGET_RLIM_INFINITY;
+        target_rlim_swap = TARGET_RLIM_INFINITY;
     else
-        return tswapl(rlim);
+        target_rlim_swap = rlim;
+    result = tswapl(target_rlim_swap);
+    
+    return result;
 }
 
 static inline abi_long copy_from_user_timeval(struct timeval *tv,