From 58fa3941a33a14decaadfdba1db0b78711643aa9 Mon Sep 17 00:00:00 2001 From: Michael Adam Date: Wed, 23 Dec 2015 18:01:23 +0100 Subject: [PATCH] s3:smbd: fix a corner case of the symlink verification Commit 7606c0db257b3f9d84da5b2bf5fbb4034cc8d77d fixes the path checks in check_reduced_name[_with_privilege]() to prevent unintended access via wide links. The fix fails to correctly treat a corner case where the share path is "/". This case is important for some real world scenarios, notably the use of the glusterfs VFS module: For the share path "/", the newly introduced checks deny all operations in the share. This change fixes the checks for the corner case. The point is that the assumptions on which the original checks are based are not true for the rootdir "/" case. This is the case where the rootdir starts _and ends_ with a slash. Hence a subdirectory does not continue with a slash after the rootdir, since the candidate path has been normalized. This fix just omits the string comparison and the next character checks in the case of rootdir "/", which is correct because we know that the candidate path is normalized and hence starts with a '/'. The patch is fairly minimal, but changes indentation, hence best viewed with 'git show -w'. A side effect is that the rootdir="/" case needs one strncmp less. BUG: https://bugzilla.samba.org/show_bug.cgi?id=11647 Pair-Programmed-With: Jose A. Rivera Signed-off-by: Michael Adam Signed-off-by: Jose A. Rivera Reviewed-by: Jeremy Allison Autobuild-User(master): Michael Adam Autobuild-Date(master): Thu Dec 24 00:57:31 CET 2015 on sn-devel-144 (cherry picked from commit ada59ec7b3a5ed0478d11da2fe0c90991d137288) --- source3/smbd/vfs.c | 78 +++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 53 insertions(+), 25 deletions(-) diff --git a/source3/smbd/vfs.c b/source3/smbd/vfs.c index edf4ee1..97eb372 100644 --- a/source3/smbd/vfs.c +++ b/source3/smbd/vfs.c @@ -976,7 +976,6 @@ NTSTATUS check_reduced_name_with_privilege(connection_struct *conn, struct smb_filename *smb_fname_cwd = NULL; struct privilege_paths *priv_paths = NULL; int ret; - bool matched; DEBUG(3,("check_reduced_name_with_privilege [%s] [%s]\n", fname, @@ -1071,18 +1070,32 @@ NTSTATUS check_reduced_name_with_privilege(connection_struct *conn, } rootdir_len = strlen(conn_rootdir); - matched = (strncmp(conn_rootdir, resolved_name, rootdir_len) == 0); - - if (!matched || (resolved_name[rootdir_len] != '/' && - resolved_name[rootdir_len] != '\0')) { - DEBUG(2, ("check_reduced_name_with_privilege: Bad access " - "attempt: %s is a symlink outside the " - "share path\n", - dir_name)); - DEBUGADD(2, ("conn_rootdir =%s\n", conn_rootdir)); - DEBUGADD(2, ("resolved_name=%s\n", resolved_name)); - status = NT_STATUS_ACCESS_DENIED; - goto err; + + /* + * In the case of rootdir_len == 1, we know that conn_rootdir is + * "/", and we also know that resolved_name starts with a slash. + * So, in this corner case, resolved_name is automatically a + * sub-directory of the conn_rootdir. Thus we can skip the string + * comparison and the next character checks (which are even + * wrong in this case). + */ + if (rootdir_len != 1) { + bool matched; + + matched = (strncmp(conn_rootdir, resolved_name, + rootdir_len) == 0); + + if (!matched || (resolved_name[rootdir_len] != '/' && + resolved_name[rootdir_len] != '\0')) { + DEBUG(2, ("check_reduced_name_with_privilege: Bad " + "access attempt: %s is a symlink outside the " + "share path\n", + dir_name)); + DEBUGADD(2, ("conn_rootdir =%s\n", conn_rootdir)); + DEBUGADD(2, ("resolved_name=%s\n", resolved_name)); + status = NT_STATUS_ACCESS_DENIED; + goto err; + } } /* Now ensure that the last component either doesn't @@ -1214,7 +1227,6 @@ NTSTATUS check_reduced_name(connection_struct *conn, const char *fname) if (!allow_widelinks || !allow_symlinks) { const char *conn_rootdir; size_t rootdir_len; - bool matched; conn_rootdir = SMB_VFS_CONNECTPATH(conn, fname); if (conn_rootdir == NULL) { @@ -1225,17 +1237,33 @@ NTSTATUS check_reduced_name(connection_struct *conn, const char *fname) } rootdir_len = strlen(conn_rootdir); - matched = (strncmp(conn_rootdir, resolved_name, - rootdir_len) == 0); - if (!matched || (resolved_name[rootdir_len] != '/' && - resolved_name[rootdir_len] != '\0')) { - DEBUG(2, ("check_reduced_name: Bad access " - "attempt: %s is a symlink outside the " - "share path\n", fname)); - DEBUGADD(2, ("conn_rootdir =%s\n", conn_rootdir)); - DEBUGADD(2, ("resolved_name=%s\n", resolved_name)); - SAFE_FREE(resolved_name); - return NT_STATUS_ACCESS_DENIED; + + /* + * In the case of rootdir_len == 1, we know that + * conn_rootdir is "/", and we also know that + * resolved_name starts with a slash. So, in this + * corner case, resolved_name is automatically a + * sub-directory of the conn_rootdir. Thus we can skip + * the string comparison and the next character checks + * (which are even wrong in this case). + */ + if (rootdir_len != 1) { + bool matched; + + matched = (strncmp(conn_rootdir, resolved_name, + rootdir_len) == 0); + if (!matched || (resolved_name[rootdir_len] != '/' && + resolved_name[rootdir_len] != '\0')) { + DEBUG(2, ("check_reduced_name: Bad access " + "attempt: %s is a symlink outside the " + "share path\n", fname)); + DEBUGADD(2, ("conn_rootdir =%s\n", + conn_rootdir)); + DEBUGADD(2, ("resolved_name=%s\n", + resolved_name)); + SAFE_FREE(resolved_name); + return NT_STATUS_ACCESS_DENIED; + } } /* Extra checks if all symlinks are disallowed. */ -- 2.5.0