Commit 3e36aba7 authored by Greg Kurz's avatar Greg Kurz
Browse files

9pfs: local: lsetxattr: don't follow symlinks 



The local_lsetxattr() callback is vulnerable to symlink attacks because
it calls lsetxattr() which follows symbolic links in all path elements but
the rightmost one.

This patch introduces a helper to emulate the non-existing fsetxattrat()
function: it is implemented with /proc/self/fd which provides a trusted
path that can be safely passed to lsetxattr().

local_lsetxattr() is converted to use this helper and opendir_nofollow().

This partly fixes CVE-2016-9602.

Signed-off-by: default avatarGreg Kurz <groug@kaod.org>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
parent 5507904e

hw/9pfs/9p-posix-acl.c

+4 −14
Original line number Diff line number Diff line
@@ -50,13 +50,8 @@ static ssize_t mp_pacl_listxattr(FsContext *ctx, const char *path, 
static int mp_pacl_setxattr(FsContext *ctx, const char *path, const char *name,

                            void *value, size_t size, int flags)

{

    char *buffer;

    int ret;



    buffer = rpath(ctx, path);

    ret = lsetxattr(buffer, MAP_ACL_ACCESS, value, size, flags);

    g_free(buffer);

    return ret;

    return local_setxattr_nofollow(ctx, path, MAP_ACL_ACCESS, value, size,

                                   flags);

}



static int mp_pacl_removexattr(FsContext *ctx,
@@ -108,13 +103,8 @@ static ssize_t mp_dacl_listxattr(FsContext *ctx, const char *path, 
static int mp_dacl_setxattr(FsContext *ctx, const char *path, const char *name,

                            void *value, size_t size, int flags)

{

    char *buffer;

    int ret;



    buffer = rpath(ctx, path);

    ret = lsetxattr(buffer, MAP_ACL_DEFAULT, value, size, flags);

    g_free(buffer);

    return ret;

    return local_setxattr_nofollow(ctx, path, MAP_ACL_DEFAULT, value, size,

                                   flags);

}



static int mp_dacl_removexattr(FsContext *ctx,

hw/9pfs/9p-util.h

+2 −0
Original line number Diff line number Diff line
@@ -48,5 +48,7 @@ int relative_openat_nofollow(int dirfd, const char *path, int flags, 
                             mode_t mode);

ssize_t fgetxattrat_nofollow(int dirfd, const char *path, const char *name,

                             void *value, size_t size);

int fsetxattrat_nofollow(int dirfd, const char *path, const char *name,

                         void *value, size_t size, int flags);



#endif

hw/9pfs/9p-xattr-user.c

+1 −7
Original line number Diff line number Diff line
@@ -67,9 +67,6 @@ static ssize_t mp_user_listxattr(FsContext *ctx, const char *path, 
static int mp_user_setxattr(FsContext *ctx, const char *path, const char *name,

                            void *value, size_t size, int flags)

{

    char *buffer;

    int ret;



    if (strncmp(name, "user.virtfs.", 12) == 0) {

        /*

         * Don't allow fetch of user.virtfs namesapce
@@ -78,10 +75,7 @@ static int mp_user_setxattr(FsContext *ctx, const char *path, const char *name, 
        errno = EACCES;

        return -1;

    }

    buffer = rpath(ctx, path);

    ret = lsetxattr(buffer, name, value, size, flags);

    g_free(buffer);

    return ret;

    return local_setxattr_nofollow(ctx, path, name, value, size, flags);

}



static int mp_user_removexattr(FsContext *ctx,

hw/9pfs/9p-xattr.c

+33 −6
Original line number Diff line number Diff line
@@ -195,18 +195,45 @@ ssize_t pt_getxattr(FsContext *ctx, const char *path, const char *name, 
    return local_getxattr_nofollow(ctx, path, name, value, size);

}



int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value,

                size_t size, int flags)

int fsetxattrat_nofollow(int dirfd, const char *filename, const char *name,

                         void *value, size_t size, int flags)

{

    char *buffer;

    char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename);

    int ret;



    buffer = rpath(ctx, path);

    ret = lsetxattr(buffer, name, value, size, flags);

    g_free(buffer);

    ret = lsetxattr(proc_path, name, value, size, flags);

    g_free(proc_path);

    return ret;

}



ssize_t local_setxattr_nofollow(FsContext *ctx, const char *path,

                                const char *name, void *value, size_t size,

                                int flags)

{

    char *dirpath = g_path_get_dirname(path);

    char *filename = g_path_get_basename(path);

    int dirfd;

    ssize_t ret = -1;



    dirfd = local_opendir_nofollow(ctx, dirpath);

    if (dirfd == -1) {

        goto out;

    }



    ret = fsetxattrat_nofollow(dirfd, filename, name, value, size, flags);

    close_preserve_errno(dirfd);

out:

    g_free(dirpath);

    g_free(filename);

    return ret;

}



int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value,

                size_t size, int flags)

{

    return local_setxattr_nofollow(ctx, path, name, value, size, flags);

}



int pt_removexattr(FsContext *ctx, const char *path, const char *name)

{

    char *buffer;

hw/9pfs/9p-xattr.h

+3 −0
Original line number Diff line number Diff line
@@ -31,6 +31,9 @@ typedef struct xattr_operations 


ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path,

                                const char *name, void *value, size_t size);

ssize_t local_setxattr_nofollow(FsContext *ctx, const char *path,

                                const char *name, void *value, size_t size,

                                int flags);



extern XattrOperations mapped_user_xattr;

extern XattrOperations passthrough_user_xattr;