[Xen-changelog] [qemu-xen stable-4.12] 9p: take write lock on fid path updates (CVE-2018-19364)

[patchbot@xxxxxxx]

commit 759d77d0395b59cc05943f83ba648830d6d35e52
Author:     Greg Kurz <groug@xxxxxxxx>
AuthorDate: Tue Nov 20 13:00:35 2018 +0100
Commit:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
CommitDate: Tue Apr 2 17:27:33 2019 +0100

    9p: take write lock on fid path updates (CVE-2018-19364)
    
    Recent commit 5b76ef50f62079a fixed a race where v9fs_co_open2() could
    possibly overwrite a fid path with v9fs_path_copy() while it is being
    accessed by some other thread, ie, use-after-free that can be detected
    by ASAN with a custom 9p client.
    
    It turns out that the same can happen at several locations where
    v9fs_path_copy() is used to set the fid path. The fix is again to
    take the write lock.
    
    Fixes CVE-2018-19364.
    
    Cc: P J P <ppandit@xxxxxxxxxx>
    Reported-by: zhibin hu <noirfate@xxxxxxxxx>
    Reviewed-by: Prasad J Pandit <pjp@xxxxxxxxxxxxxxxxx>
    Signed-off-by: Greg Kurz <groug@xxxxxxxx>
    (cherry picked from commit 5b3c77aa581ebb215125c84b0742119483571e55)
---
 hw/9pfs/9p.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index eef289e394..267a25533b 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -1391,7 +1391,9 @@ static void coroutine_fn v9fs_walk(void *opaque)
             err = -EINVAL;
             goto out;
         }
+        v9fs_path_write_lock(s);
         v9fs_path_copy(&fidp->path, &path);
+        v9fs_path_unlock(s);
     } else {
         newfidp = alloc_fid(s, newfid);
         if (newfidp == NULL) {
@@ -2160,6 +2162,7 @@ static void coroutine_fn v9fs_create(void *opaque)
     V9fsString extension;
     int iounit;
     V9fsPDU *pdu = opaque;
+    V9fsState *s = pdu->s;
 
     v9fs_path_init(&path);
     v9fs_string_init(&name);
@@ -2200,7 +2203,9 @@ static void coroutine_fn v9fs_create(void *opaque)
         if (err < 0) {
             goto out;
         }
+        v9fs_path_write_lock(s);
         v9fs_path_copy(&fidp->path, &path);
+        v9fs_path_unlock(s);
         err = v9fs_co_opendir(pdu, fidp);
         if (err < 0) {
             goto out;
@@ -2216,7 +2221,9 @@ static void coroutine_fn v9fs_create(void *opaque)
         if (err < 0) {
             goto out;
         }
+        v9fs_path_write_lock(s);
         v9fs_path_copy(&fidp->path, &path);
+        v9fs_path_unlock(s);
     } else if (perm & P9_STAT_MODE_LINK) {
         int32_t ofid = atoi(extension.data);
         V9fsFidState *ofidp = get_fid(pdu, ofid);
@@ -2234,7 +2241,9 @@ static void coroutine_fn v9fs_create(void *opaque)
             fidp->fid_type = P9_FID_NONE;
             goto out;
         }
+        v9fs_path_write_lock(s);
         v9fs_path_copy(&fidp->path, &path);
+        v9fs_path_unlock(s);
         err = v9fs_co_lstat(pdu, &fidp->path, &stbuf);
         if (err < 0) {
             fidp->fid_type = P9_FID_NONE;
@@ -2272,7 +2281,9 @@ static void coroutine_fn v9fs_create(void *opaque)
         if (err < 0) {
             goto out;
         }
+        v9fs_path_write_lock(s);
         v9fs_path_copy(&fidp->path, &path);
+        v9fs_path_unlock(s);
     } else if (perm & P9_STAT_MODE_NAMED_PIPE) {
         err = v9fs_co_mknod(pdu, fidp, &name, fidp->uid, -1,
                             0, S_IFIFO | (perm & 0777), &stbuf);
@@ -2283,7 +2294,9 @@ static void coroutine_fn v9fs_create(void *opaque)
         if (err < 0) {
             goto out;
         }
+        v9fs_path_write_lock(s);
         v9fs_path_copy(&fidp->path, &path);
+        v9fs_path_unlock(s);
     } else if (perm & P9_STAT_MODE_SOCKET) {
         err = v9fs_co_mknod(pdu, fidp, &name, fidp->uid, -1,
                             0, S_IFSOCK | (perm & 0777), &stbuf);
@@ -2294,7 +2307,9 @@ static void coroutine_fn v9fs_create(void *opaque)
         if (err < 0) {
             goto out;
         }
+        v9fs_path_write_lock(s);
         v9fs_path_copy(&fidp->path, &path);
+        v9fs_path_unlock(s);
     } else {
         err = v9fs_co_open2(pdu, fidp, &name, -1,
                             omode_to_uflags(mode)|O_CREAT, perm, &stbuf);
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.12

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