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Violators will be prosecuted for from ; Mon, 27 Feb 2017 23:00:45 -0000 From: Greg Kurz Date: Tue, 28 Feb 2017 00:00:03 +0100 In-Reply-To: <1488236421-30983-1-git-send-email-groug@kaod.org> References: <1488236421-30983-1-git-send-email-groug@kaod.org> Message-Id: <1488236421-30983-14-git-send-email-groug@kaod.org> Subject: [Qemu-devel] [PULL 13/31] 9pfs: local: lremovexattr: don't follow symlinks List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org Cc: Peter Maydell , "Aneesh Kumar K.V" , Greg Kurz The local_lremovexattr() callback is vulnerable to symlink attacks because it calls lremovexattr() which follows symbolic links in all path elements but the rightmost one. This patch introduces a helper to emulate the non-existing fremovexattrat() function: it is implemented with /proc/self/fd which provides a trusted path that can be safely passed to lremovexattr(). local_lremovexattr() is converted to use this helper and opendir_nofollow(). This partly fixes CVE-2016-9602. Signed-off-by: Greg Kurz Reviewed-by: Stefan Hajnoczi --- hw/9pfs/9p-posix-acl.c | 10 ++-------- hw/9pfs/9p-xattr-user.c | 8 +------- hw/9pfs/9p-xattr.c | 36 +++++++++++++++++++++++++++++++----- hw/9pfs/9p-xattr.h | 2 ++ 4 files changed, 36 insertions(+), 20 deletions(-) diff --git a/hw/9pfs/9p-posix-acl.c b/hw/9pfs/9p-posix-acl.c index 0154e2a7605f..bbf89064f7ae 100644 --- a/hw/9pfs/9p-posix-acl.c +++ b/hw/9pfs/9p-posix-acl.c @@ -58,10 +58,8 @@ static int mp_pacl_removexattr(FsContext *ctx, const char *path, const char *name) { int ret; - char *buffer; - buffer = rpath(ctx, path); - ret = lremovexattr(buffer, MAP_ACL_ACCESS); + ret = local_removexattr_nofollow(ctx, path, MAP_ACL_ACCESS); if (ret == -1 && errno == ENODATA) { /* * We don't get ENODATA error when trying to remove a @@ -71,7 +69,6 @@ static int mp_pacl_removexattr(FsContext *ctx, errno = 0; ret = 0; } - g_free(buffer); return ret; } @@ -111,10 +108,8 @@ static int mp_dacl_removexattr(FsContext *ctx, const char *path, const char *name) { int ret; - char *buffer; - buffer = rpath(ctx, path); - ret = lremovexattr(buffer, MAP_ACL_DEFAULT); + ret = local_removexattr_nofollow(ctx, path, MAP_ACL_DEFAULT); if (ret == -1 && errno == ENODATA) { /* * We don't get ENODATA error when trying to remove a @@ -124,7 +119,6 @@ static int mp_dacl_removexattr(FsContext *ctx, errno = 0; ret = 0; } - g_free(buffer); return ret; } diff --git a/hw/9pfs/9p-xattr-user.c b/hw/9pfs/9p-xattr-user.c index 1840a5db66f3..2c90817b75a6 100644 --- a/hw/9pfs/9p-xattr-user.c +++ b/hw/9pfs/9p-xattr-user.c @@ -81,9 +81,6 @@ static int mp_user_setxattr(FsContext *ctx, const char *path, const char *name, static int mp_user_removexattr(FsContext *ctx, const char *path, const char *name) { - char *buffer; - int ret; - if (strncmp(name, "user.virtfs.", 12) == 0) { /* * Don't allow fetch of user.virtfs namesapce @@ -92,10 +89,7 @@ static int mp_user_removexattr(FsContext *ctx, errno = EACCES; return -1; } - buffer = rpath(ctx, path); - ret = lremovexattr(buffer, name); - g_free(buffer); - return ret; + return local_removexattr_nofollow(ctx, path, name); } XattrOperations mapped_user_xattr = { diff --git a/hw/9pfs/9p-xattr.c b/hw/9pfs/9p-xattr.c index a0167dd4d898..eec160b3c2ac 100644 --- a/hw/9pfs/9p-xattr.c +++ b/hw/9pfs/9p-xattr.c @@ -234,17 +234,43 @@ int pt_setxattr(FsContext *ctx, const char *path, const char *name, void *value, return local_setxattr_nofollow(ctx, path, name, value, size, flags); } -int pt_removexattr(FsContext *ctx, const char *path, const char *name) +static ssize_t fremovexattrat_nofollow(int dirfd, const char *filename, + const char *name) { - char *buffer; + char *proc_path = g_strdup_printf("/proc/self/fd/%d/%s", dirfd, filename); int ret; - buffer = rpath(ctx, path); - ret = lremovexattr(path, name); - g_free(buffer); + ret = lremovexattr(proc_path, name); + g_free(proc_path); return ret; } +ssize_t local_removexattr_nofollow(FsContext *ctx, const char *path, + const char *name) +{ + 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 = fremovexattrat_nofollow(dirfd, filename, name); + close_preserve_errno(dirfd); +out: + g_free(dirpath); + g_free(filename); + return ret; +} + +int pt_removexattr(FsContext *ctx, const char *path, const char *name) +{ + return local_removexattr_nofollow(ctx, path, name); +} + ssize_t notsup_getxattr(FsContext *ctx, const char *path, const char *name, void *value, size_t size) { diff --git a/hw/9pfs/9p-xattr.h b/hw/9pfs/9p-xattr.h index 7558970d8511..0d83996575e1 100644 --- a/hw/9pfs/9p-xattr.h +++ b/hw/9pfs/9p-xattr.h @@ -34,6 +34,8 @@ ssize_t local_getxattr_nofollow(FsContext *ctx, const char *path, ssize_t local_setxattr_nofollow(FsContext *ctx, const char *path, const char *name, void *value, size_t size, int flags); +ssize_t local_removexattr_nofollow(FsContext *ctx, const char *path, + const char *name); extern XattrOperations mapped_user_xattr; extern XattrOperations passthrough_user_xattr; -- 2.7.4