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copy: put a depth limit on copying file system trees recursively

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This is a safety net against bind mount cycles, as such pick it
relatively high at 2048 for now.

As suggested by @filbranden on #9213
This commit is contained in:
Lennart Poettering 2018-06-07 13:24:03 +02:00
parent f6a77804c9
commit 575a07d2dc
1 changed files with 17 additions and 6 deletions
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23
src/basic/copy.c
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@ -37,7 +37,12 @@
#include "user-util.h"
#include "xattr-util.h"
#define COPY_BUFFER_SIZE (16*1024u)
#define COPY_BUFFER_SIZE (16U*1024U)
/* A safety net for descending recursively into file system trees to copy. On Linux PATH_MAX is 4096, which means the
* deepest valid path one can build is around 2048, which we hence use as a safety net here, to not spin endlessly in
* case of bind mount cycles and suchlike. */
#define COPY_DEPTH_MAX 2048U
static ssize_t try_copy_file_range(
int fd_in, loff_t *off_in,
@ -480,6 +485,7 @@ static int fd_copy_directory(
int dt,
const char *to,
dev_t original_device,
unsigned depth_left,
uid_t override_uid,
gid_t override_gid,
CopyFlags copy_flags) {
@ -493,6 +499,9 @@ static int fd_copy_directory(
assert(st);
assert(to);
if (depth_left == 0)
return -ENAMETOOLONG;
if (from)
fdf = openat(df, from, O_RDONLY|O_DIRECTORY|O_CLOEXEC|O_NOCTTY|O_NOFOLLOW);
else
@ -546,7 +555,9 @@ static int fd_copy_directory(
* • The main reason we do this check at all is to protect ourselves from bind mount cycles,
* where we really want to avoid descending down in all eternity. However the .st_dev check
* is usually not sufficient for this protection anyway, as bind mount cycles from the same
* file system onto itself can't be detected that way.
* file system onto itself can't be detected that way. (Note we also do a recursion depth
* check, which is probably the better protection in this regard, which is why
* COPY_SAME_MOUNT is optional).
*/
if (FLAGS_SET(copy_flags, COPY_SAME_MOUNT)) {
@ -560,7 +571,7 @@ static int fd_copy_directory(
continue;
}
q = fd_copy_directory(dirfd(d), de->d_name, &buf, fdt, de->d_name, original_device, override_uid, override_gid, copy_flags);
q = fd_copy_directory(dirfd(d), de->d_name, &buf, fdt, de->d_name, original_device, depth_left-1, override_uid, override_gid, copy_flags);
} else if (S_ISREG(buf.st_mode))
q = fd_copy_regular(dirfd(d), de->d_name, &buf, fdt, de->d_name, override_uid, override_gid, copy_flags);
else if (S_ISLNK(buf.st_mode))
@ -612,7 +623,7 @@ int copy_tree_at(int fdf, const char *from, int fdt, const char *to, uid_t overr
if (S_ISREG(st.st_mode))
return fd_copy_regular(fdf, from, &st, fdt, to, override_uid, override_gid, copy_flags);
else if (S_ISDIR(st.st_mode))
return fd_copy_directory(fdf, from, &st, fdt, to, st.st_dev, override_uid, override_gid, copy_flags);
return fd_copy_directory(fdf, from, &st, fdt, to, st.st_dev, COPY_DEPTH_MAX, override_uid, override_gid, copy_flags);
else if (S_ISLNK(st.st_mode))
return fd_copy_symlink(fdf, from, &st, fdt, to, override_uid, override_gid, copy_flags);
else if (S_ISFIFO(st.st_mode))
@ -639,7 +650,7 @@ int copy_directory_fd(int dirfd, const char *to, CopyFlags copy_flags) {
if (!S_ISDIR(st.st_mode))
return -ENOTDIR;
return fd_copy_directory(dirfd, NULL, &st, AT_FDCWD, to, st.st_dev, UID_INVALID, GID_INVALID, copy_flags);
return fd_copy_directory(dirfd, NULL, &st, AT_FDCWD, to, st.st_dev, COPY_DEPTH_MAX, UID_INVALID, GID_INVALID, copy_flags);
}
int copy_directory(const char *from, const char *to, CopyFlags copy_flags) {
@ -654,7 +665,7 @@ int copy_directory(const char *from, const char *to, CopyFlags copy_flags) {
if (!S_ISDIR(st.st_mode))
return -ENOTDIR;
return fd_copy_directory(AT_FDCWD, from, &st, AT_FDCWD, to, st.st_dev, UID_INVALID, GID_INVALID, copy_flags);
return fd_copy_directory(AT_FDCWD, from, &st, AT_FDCWD, to, st.st_dev, COPY_DEPTH_MAX, UID_INVALID, GID_INVALID, copy_flags);
}
int copy_file_fd(const char *from, int fdt, CopyFlags copy_flags) {