verify_path: disallow symlinks in .gitmodules

There are a few reasons it's not a good idea to make
.gitmodules a symlink, including:

  1. It won't be portable to systems without symlinks.

  2. It may behave inconsistently, since Git may look at
     this file in the index or a tree without bothering to
     resolve any symbolic links. We don't do this _yet_, but
     the config infrastructure is there and it's planned for
     the future.

With some clever code, we could make (2) work. And some
people may not care about (1) if they only work on one
platform. But there are a few security reasons to simply
disallow it:

  a. A symlinked .gitmodules file may circumvent any fsck
     checks of the content.

  b. Git may read and write from the on-disk file without
     sanity checking the symlink target. So for example, if
     you link ".gitmodules" to "../oops" and run "git
     submodule add", we'll write to the file "oops" outside
     the repository.

Again, both of those are problems that _could_ be solved
with sufficient code, but given the complications in (1) and
(2), we're better off just outlawing it explicitly.

Note the slightly tricky call to verify_path() in
update-index's update_one(). There we may not have a mode if
we're not updating from the filesystem (e.g., we might just
be removing the file). Passing "0" as the mode there works
fine; since it's not a symlink, we'll just skip the extra
checks.

Signed-off-by: Jeff King <peff@peff.net>

diff --git a/apply.c b/apply.c
index f8bf0bd9323d1155e9b382eacc8bdae18eb0d2b2..b96d3755950f09e3c1661b59a3247060388868aa 100644 (file)
--- a/apply.c
+++ b/apply.c
@@ -3867,9 +3867,9 @@ static int check_unsafe_path(struct patch *patch)
        if (!patch->is_delete)
                new_name = patch->new_name;
 
-       if (old_name && !verify_path(old_name))
+       if (old_name && !verify_path(old_name, patch->old_mode))
                return error(_("invalid path '%s'"), old_name);
-       if (new_name && !verify_path(new_name))
+       if (new_name && !verify_path(new_name, patch->new_mode))
                return error(_("invalid path '%s'"), new_name);
        return 0;
 }

diff --git a/builtin/update-index.c b/builtin/update-index.c
index 8d152ded779ad48426d6956f30a4ef6c7ea9238c..19216595fbb917d06d51a42a85d0975d903948a9 100644 (file)
--- a/builtin/update-index.c
+++ b/builtin/update-index.c
@@ -399,7 +399,7 @@ static int add_cacheinfo(unsigned int mode, const struct object_id *oid,
        int size, len, option;
        struct cache_entry *ce;
 
-       if (!verify_path(path))
+       if (!verify_path(path, mode))
                return error("Invalid path '%s'", path);
 
        len = strlen(path);
@@ -452,7 +452,7 @@ static void update_one(const char *path)
                stat_errno = errno;
        } /* else stat is valid */
 
-       if (!verify_path(path)) {
+       if (!verify_path(path, st.st_mode)) {
                fprintf(stderr, "Ignoring path %s\n", path);
                return;
        }
@@ -543,7 +543,7 @@ static void read_index_info(int nul_term_line)
                        path_name = uq.buf;
                }
 
-               if (!verify_path(path_name)) {
+               if (!verify_path(path_name, mode)) {
                        fprintf(stderr, "Ignoring path %s\n", path_name);
                        continue;
                }

diff --git a/cache.h b/cache.h
index 041c0fb2611152354ec3d2346a001f75cd79a830..5a44f79e263b650472b650b72de3b5430243f273 100644 (file)
--- a/cache.h
+++ b/cache.h
@@ -598,7 +598,7 @@ extern int read_index_unmerged(struct index_state *);
 extern int write_locked_index(struct index_state *, struct lock_file *lock, unsigned flags);
 extern int discard_index(struct index_state *);
 extern int unmerged_index(const struct index_state *);
-extern int verify_path(const char *path);
+extern int verify_path(const char *path, unsigned mode);
 extern int strcmp_offset(const char *s1, const char *s2, size_t *first_change);
 extern int index_dir_exists(struct index_state *istate, const char *name, int namelen);
 extern void adjust_dirname_case(struct index_state *istate, char *name);

diff --git a/read-cache.c b/read-cache.c
index 333e0c542967814fcb3e71fd4cec973548b4f567..aa99f1f797985d4128af3716b8e4257e4ba2d37c 100644 (file)
--- a/read-cache.c
+++ b/read-cache.c
@@ -732,7 +732,7 @@ struct cache_entry *make_cache_entry(unsigned int mode,
        int size, len;
        struct cache_entry *ce, *ret;
 
-       if (!verify_path(path)) {
+       if (!verify_path(path, mode)) {
                error("Invalid path '%s'", path);
                return NULL;
        }
@@ -796,7 +796,7 @@ int ce_same_name(const struct cache_entry *a, const struct cache_entry *b)
  * Also, we don't want double slashes or slashes at the
  * end that can make pathnames ambiguous.
  */
-static int verify_dotfile(const char *rest)
+static int verify_dotfile(const char *rest, unsigned mode)
 {
        /*
         * The first character was '.', but that
@@ -814,6 +814,9 @@ static int verify_dotfile(const char *rest)
         * case-insensitively here, even if ignore_case is not set.
         * This outlaws ".GIT" everywhere out of an abundance of caution,
         * since there's really no good reason to allow it.
+        *
+        * Once we've seen ".git", we can also find ".gitmodules", etc (also
+        * case-insensitively).
         */
        case 'g':
        case 'G':
@@ -823,6 +826,12 @@ static int verify_dotfile(const char *rest)
                        break;
                if (rest[3] == '\0' || is_dir_sep(rest[3]))
                        return 0;
+               if (S_ISLNK(mode)) {
+                       rest += 3;
+                       if (skip_iprefix(rest, "modules", &rest) &&
+                           (*rest == '\0' || is_dir_sep(*rest)))
+                               return 0;
+               }
                break;
        case '.':
                if (rest[1] == '\0' || is_dir_sep(rest[1]))
@@ -831,7 +840,7 @@ static int verify_dotfile(const char *rest)
        return 1;
 }
 
-int verify_path(const char *path)
+int verify_path(const char *path, unsigned mode)
 {
        char c;
 
@@ -844,12 +853,25 @@ int verify_path(const char *path)
                        return 1;
                if (is_dir_sep(c)) {
 inside:
-                       if (protect_hfs && is_hfs_dotgit(path))
-                               return 0;
-                       if (protect_ntfs && is_ntfs_dotgit(path))
-                               return 0;
+                       if (protect_hfs) {
+                               if (is_hfs_dotgit(path))
+                                       return 0;
+                               if (S_ISLNK(mode)) {
+                                       if (is_hfs_dotgitmodules(path))
+                                               return 0;
+                               }
+                       }
+                       if (protect_ntfs) {
+                               if (is_ntfs_dotgit(path))
+                                       return 0;
+                               if (S_ISLNK(mode)) {
+                                       if (is_ntfs_dotgitmodules(path))
+                                               return 0;
+                               }
+                       }
+
                        c = *path++;
-                       if ((c == '.' && !verify_dotfile(path)) ||
+                       if ((c == '.' && !verify_dotfile(path, mode)) ||
                            is_dir_sep(c) || c == '\0')
                                return 0;
                }
@@ -1166,7 +1188,7 @@ static int add_index_entry_with_check(struct index_state *istate, struct cache_e
 
        if (!ok_to_add)
                return -1;
-       if (!verify_path(ce->name))
+       if (!verify_path(ce->name, ce->ce_mode))
                return error("Invalid path '%s'", ce->name);
 
        if (!skip_df_check &&