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tree-walk: learn get_tree_entry_follow_symlinks

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Add a new function, get_tree_entry_follow_symlinks, to tree-walk.[ch].
The function is not yet used.  It will be used to implement git
cat-file --batch --follow-symlinks.

The function locates an object by path, following symlinks in the
repository.  If the symlinks lead outside the repository, the function
reports this to the caller.

Signed-off-by: David Turner <dturner@twopensource.com>
Signed-off-by: Ramsay Jones <ramsay@ramsay1.demon.co.uk>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
David Turner 2015-05-20 13:03:38 -04:00 committed by Junio C Hamano
parent 8440f74997
commit 275721c267
2 changed files with 224 additions and 0 deletions
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206
tree-walk.c
View File

@ -415,6 +415,12 @@ int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info)
return error;
}
struct dir_state {
void *tree;
unsigned long size;
unsigned char sha1[20];
};
static int find_tree_entry(struct tree_desc *t, const char *name, unsigned char *result, unsigned *mode)
{
int namelen = strlen(name);
@ -478,6 +484,206 @@ int get_tree_entry(const unsigned char *tree_sha1, const char *name, unsigned ch
return retval;
}
/*
* This is Linux's built-in max for the number of symlinks to follow.
* That limit, of course, does not affect git, but it's a reasonable
* choice.
*/
#define GET_TREE_ENTRY_FOLLOW_SYMLINKS_MAX_LINKS 40
/**
* Find a tree entry by following symlinks in tree_sha (which is
* assumed to be the root of the repository). In the event that a
* symlink points outside the repository (e.g. a link to /foo or a
* root-level link to ../foo), the portion of the link which is
* outside the repository will be returned in result_path, and *mode
* will be set to 0. It is assumed that result_path is uninitialized.
* If there are no symlinks, or the end result of the symlink chain
* points to an object inside the repository, result will be filled in
* with the sha1 of the found object, and *mode will hold the mode of
* the object.
*
* See the code for enum follow_symlink_result for a description of
* the return values.
*/
enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_sha1, const char *name, unsigned char *result, struct strbuf *result_path, unsigned *mode)
{
int retval = MISSING_OBJECT;
struct dir_state *parents = NULL;
size_t parents_alloc = 0;
ssize_t parents_nr = 0;
unsigned char current_tree_sha1[20];
struct strbuf namebuf = STRBUF_INIT;
struct tree_desc t;
int follows_remaining = GET_TREE_ENTRY_FOLLOW_SYMLINKS_MAX_LINKS;
int i;
init_tree_desc(&t, NULL, 0UL);
strbuf_init(result_path, 0);
strbuf_addstr(&namebuf, name);
hashcpy(current_tree_sha1, tree_sha1);
while (1) {
int find_result;
char *first_slash;
char *remainder = NULL;
if (!t.buffer) {
void *tree;
unsigned char root[20];
unsigned long size;
tree = read_object_with_reference(current_tree_sha1,
tree_type, &size,
root);
if (!tree)
goto done;
ALLOC_GROW(parents, parents_nr + 1, parents_alloc);
parents[parents_nr].tree = tree;
parents[parents_nr].size = size;
hashcpy(parents[parents_nr].sha1, root);
parents_nr++;
if (namebuf.buf[0] == '\0') {
hashcpy(result, root);
retval = FOUND;
goto done;
}
if (!size)
goto done;
/* descend */
init_tree_desc(&t, tree, size);
}
/* Handle symlinks to e.g. a//b by removing leading slashes */
while (namebuf.buf[0] == '/') {
strbuf_remove(&namebuf, 0, 1);
}
/* Split namebuf into a first component and a remainder */
if ((first_slash = strchr(namebuf.buf, '/'))) {
*first_slash = 0;
remainder = first_slash + 1;
}
if (!strcmp(namebuf.buf, "..")) {
struct dir_state *parent;
/*
* We could end up with .. in the namebuf if it
* appears in a symlink.
*/
if (parents_nr == 1) {
if (remainder)
*first_slash = '/';
strbuf_add(result_path, namebuf.buf,
namebuf.len);
*mode = 0;
retval = FOUND;
goto done;
}
parent = &parents[parents_nr - 1];
free(parent->tree);
parents_nr--;
parent = &parents[parents_nr - 1];
init_tree_desc(&t, parent->tree, parent->size);
strbuf_remove(&namebuf, 0, remainder ? 3 : 2);
continue;
}
/* We could end up here via a symlink to dir/.. */
if (namebuf.buf[0] == '\0') {
hashcpy(result, parents[parents_nr - 1].sha1);
retval = FOUND;
goto done;
}
/* Look up the first (or only) path component in the tree. */
find_result = find_tree_entry(&t, namebuf.buf,
current_tree_sha1, mode);
if (find_result) {
goto done;
}
if (S_ISDIR(*mode)) {
if (!remainder) {
hashcpy(result, current_tree_sha1);
retval = FOUND;
goto done;
}
/* Descend the tree */
t.buffer = NULL;
strbuf_remove(&namebuf, 0,
1 + first_slash - namebuf.buf);
} else if (S_ISREG(*mode)) {
if (!remainder) {
hashcpy(result, current_tree_sha1);
retval = FOUND;
} else {
retval = NOT_DIR;
}
goto done;
} else if (S_ISLNK(*mode)) {
/* Follow a symlink */
unsigned long link_len;
size_t len;
char *contents, *contents_start;
struct dir_state *parent;
enum object_type type;
if (follows_remaining-- == 0) {
/* Too many symlinks followed */
retval = SYMLINK_LOOP;
goto done;
}
/*
* At this point, we have followed at a least
* one symlink, so on error we need to report this.
*/
retval = DANGLING_SYMLINK;
contents = read_sha1_file(current_tree_sha1, &type,
&link_len);
if (!contents)
goto done;
if (contents[0] == '/') {
strbuf_addstr(result_path, contents);
free(contents);
*mode = 0;
retval = FOUND;
goto done;
}
if (remainder)
len = first_slash - namebuf.buf;
else
len = namebuf.len;
contents_start = contents;
parent = &parents[parents_nr - 1];
init_tree_desc(&t, parent->tree, parent->size);
strbuf_splice(&namebuf, 0, len,
contents_start, link_len);
if (remainder)
namebuf.buf[link_len] = '/';
free(contents);
}
}
done:
for (i = 0; i < parents_nr; i++)
free(parents[i].tree);
free(parents);
strbuf_release(&namebuf);
return retval;
}
static int match_entry(const struct pathspec_item *item,
const struct name_entry *entry, int pathlen,
const char *match, int matchlen,

18
tree-walk.h
View File

@ -40,6 +40,24 @@ struct traverse_info;
typedef int (*traverse_callback_t)(int n, unsigned long mask, unsigned long dirmask, struct name_entry *entry, struct traverse_info *);
int traverse_trees(int n, struct tree_desc *t, struct traverse_info *info);
enum follow_symlinks_result {
FOUND = 0, /* This includes out-of-tree links */
MISSING_OBJECT = -1, /* The initial symlink is missing */
DANGLING_SYMLINK = -2, /*
* The initial symlink is there, but
* (transitively) points to a missing
* in-tree file
*/
SYMLINK_LOOP = -3,
NOT_DIR = -4, /*
* Somewhere along the symlink chain, a path is
* requested which contains a file as a
* non-final element.
*/
};
enum follow_symlinks_result get_tree_entry_follow_symlinks(unsigned char *tree_sha1, const char *name, unsigned char *result, struct strbuf *result_path, unsigned *mode);
struct traverse_info {
struct traverse_info *prev;
struct name_entry name;