diff mbox series

[v2,1/3] linux-user: Fix openat() emulation to correctly detect accesses to /proc

Message ID 20230801230842.414421-2-deller@gmx.de
State New
Headers show
Series linux-user: /proc/cpuinfo fix and content emulation for arm | expand

Commit Message

Helge Deller Aug. 1, 2023, 11:08 p.m. UTC 
In qemu we catch accesses to files like /proc/cpuinfo or /proc/net/route
and return to the guest contents which would be visible on a real system
(instead what the host would show).

This patch fixes a bug, where for example the accesses
    cat /proc////cpuinfo
or
    cd /proc && cat cpuinfo
will not be recognized by qemu and where qemu will wrongly show
the contents of the host's /proc/cpuinfo file.

Signed-off-by: Helge Deller <deller@gmx.de>

--
v3:
- use g_autofree on returned value from realpath

v2:
- use g_autofree instead of pathname on stack
  Daniel P. Berrangé requested to not put buffers on stack.
  Using g_autofree keeps code much cleaner than using
  extended semantics of realpath(), unless I can use g_autofree
  on malloced area from realpath().
---
 linux-user/syscall.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

--
2.41.0

Comments

Daniel P. Berrangé Aug. 2, 2023, 8:16 a.m. UTC | #1 
On Wed, Aug 02, 2023 at 01:08:40AM +0200, Helge Deller wrote:
> In qemu we catch accesses to files like /proc/cpuinfo or /proc/net/route
> and return to the guest contents which would be visible on a real system
> (instead what the host would show).
> 
> This patch fixes a bug, where for example the accesses
>     cat /proc////cpuinfo
> or
>     cd /proc && cat cpuinfo
> will not be recognized by qemu and where qemu will wrongly show
> the contents of the host's /proc/cpuinfo file.
> 
> Signed-off-by: Helge Deller <deller@gmx.de>
> 
> --
> v3:
> - use g_autofree on returned value from realpath
> 
> v2:
> - use g_autofree instead of pathname on stack
>   Daniel P. Berrangé requested to not put buffers on stack.
>   Using g_autofree keeps code much cleaner than using
>   extended semantics of realpath(), unless I can use g_autofree
>   on malloced area from realpath().
> ---
>  linux-user/syscall.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


With regards,
Daniel
diff mbox series

Patch

diff --git a/linux-user/syscall.c b/linux-user/syscall.c
index 95727a816a..1ec7d27e37 100644
--- a/linux-user/syscall.c
+++ b/linux-user/syscall.c
@@ -8539,9 +8539,12 @@  static int open_hardware(CPUArchState *cpu_env, int fd)
 }
 #endif

-int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *pathname,
+
+int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *fname,
                     int flags, mode_t mode, bool safe)
 {
+    g_autofree char *proc_name = NULL;
+    const char *pathname;
     struct fake_open {
         const char *filename;
         int (*fill)(CPUArchState *cpu_env, int fd);
@@ -8567,6 +8570,14 @@  int do_guest_openat(CPUArchState *cpu_env, int dirfd, const char *pathname,
         { NULL, NULL, NULL }
     };

+    /* if this is a file from /proc/ filesystem, expand full name */
+    proc_name = realpath(fname, NULL);
+    if (proc_name && strncmp(proc_name, "/proc/", 6) == 0) {
+        pathname = proc_name;
+    } else {
+        pathname = fname;
+    }
+
     if (is_proc_myself(pathname, "exe")) {
         if (safe) {
             return safe_openat(dirfd, exec_path, flags, mode);