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Fix readlink implementation, add more tests

fixes
Antonio SJ Musumeci 2 days ago
parent
89c2ada323
commit
6d96e55fff
2 changed files with 234 additions and 5 deletions
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  1. 20
      src/fuse_readlink.cpp
  2. 219
      tests/TEST_readlink_semantics

20
src/fuse_readlink.cpp
View File

@ -27,6 +27,7 @@
#include "fuse.h" #include "fuse.h"
#include <algorithm>
#include <cstring> #include <cstring>
@ -39,11 +40,12 @@ _readlink_core_standard(const fs::path &fullpath_,
{ {
int rv; int rv;
rv = fs::readlink(fullpath_,buf_,(bufsize_ - 1));
rv = fs::readlink(fullpath_,buf_,bufsize_);
if(rv < 0) if(rv < 0)
return rv; return rv;
buf_[rv] = '\0';
if((size_t)rv < bufsize_)
buf_[rv] = '\0';
return 0; return 0;
} }
@ -56,17 +58,23 @@ _readlink_core_symlinkify(const fs::path &fullpath_,
const time_t symlinkify_timeout_) const time_t symlinkify_timeout_)
{ {
int rv; int rv;
size_t n;
std::string fullpath_str;
struct stat st; struct stat st;
rv = fs::lstat(fullpath_,&st);
fullpath_str = fullpath_.string();
rv = fs::lstat(fullpath_str,&st);
if(rv < 0) if(rv < 0)
return rv; return rv;
if(!symlinkify::can_be_symlink(st,symlinkify_timeout_)) if(!symlinkify::can_be_symlink(st,symlinkify_timeout_))
return ::_readlink_core_standard(fullpath_,buf_,bufsize_); return ::_readlink_core_standard(fullpath_,buf_,bufsize_);
strncpy(buf_,fullpath_.c_str(),(bufsize_ - 1));
buf_[bufsize_ - 1] = '\0';
n = std::min(fullpath_str.size(),bufsize_);
memcpy(buf_,fullpath_str.c_str(),n);
if(n < bufsize_)
buf_[n] = '\0';
return 0; return 0;
} }
@ -106,6 +114,8 @@ _readlink(const Policy::Search &searchFunc_,
rv = searchFunc_(ibranches_,fusepath_,obranches); rv = searchFunc_(ibranches_,fusepath_,obranches);
if(rv < 0) if(rv < 0)
return rv; return rv;
if(obranches.empty())
return -ENOENT;
return ::_readlink_core(obranches[0]->path, return ::_readlink_core(obranches[0]->path,
fusepath_, fusepath_,

219
tests/TEST_readlink_semantics
View File

@ -0,0 +1,219 @@
#!/usr/bin/env python3
import ctypes
import errno
import os
import sys
import tempfile
libc = ctypes.CDLL(None, use_errno=True)
libc.readlink.argtypes = [ctypes.c_char_p, ctypes.c_char_p, ctypes.c_size_t]
libc.readlink.restype = ctypes.c_ssize_t
def readlink_raw(path: str, bufsiz: int):
buf = ctypes.create_string_buffer(bufsiz)
ctypes.set_errno(0)
rv = libc.readlink(path.encode(), buf, bufsiz)
err = ctypes.get_errno()
return rv, err, bytes(buf)
def compare_case(name: str,
merge_path: str,
native_path: str,
bufsiz: int,
expect_errno: int = None):
m_rv, m_errno, m_buf = readlink_raw(merge_path, bufsiz)
n_rv, n_errno, n_buf = readlink_raw(native_path, bufsiz)
if m_rv != n_rv:
return f"{name}: return mismatch mergerfs={m_rv} native={n_rv}"
if m_errno != n_errno:
return f"{name}: errno mismatch mergerfs={m_errno} native={n_errno}"
if m_rv >= 0 and m_buf != n_buf:
return f"{name}: buffer mismatch mergerfs={m_buf!r} native={n_buf!r}"
if expect_errno is not None and n_errno != expect_errno:
return f"{name}: expected errno={expect_errno}, got errno={n_errno}"
return None
def main():
if len(sys.argv) != 2:
print("usage: TEST_readlink_semantics <mountpoint>", file=sys.stderr)
return 1
mount = sys.argv[1]
target = "target-abcdefghijklmnopqrstuvwxyz"
with tempfile.TemporaryDirectory() as native_dir:
paths = {
"merge_link": os.path.join(mount, "readlink-semantics-link"),
"native_link": os.path.join(native_dir, "readlink-semantics-link"),
"merge_regular": os.path.join(mount, "readlink-semantics-regular"),
"native_regular": os.path.join(native_dir, "readlink-semantics-regular"),
"merge_notdir": os.path.join(mount, "readlink-semantics-notdir"),
"native_notdir": os.path.join(native_dir, "readlink-semantics-notdir"),
"merge_loop": os.path.join(mount, "readlink-semantics-loop"),
"native_loop": os.path.join(native_dir, "readlink-semantics-loop"),
"merge_private_dir": os.path.join(mount, "readlink-semantics-private"),
"native_private_dir": os.path.join(native_dir, "readlink-semantics-private"),
}
paths["merge_private_link"] = os.path.join(paths["merge_private_dir"], "link")
paths["native_private_link"] = os.path.join(paths["native_private_dir"], "link")
for p in (
paths["merge_private_link"],
paths["merge_link"],
paths["merge_regular"],
paths["merge_notdir"],
paths["merge_loop"],
):
try:
os.unlink(p)
except FileNotFoundError:
pass
try:
os.rmdir(paths["merge_private_dir"])
except FileNotFoundError:
pass
except OSError:
pass
os.symlink(target, paths["merge_link"])
os.symlink(target, paths["native_link"])
with open(paths["merge_regular"], "w", encoding="ascii"):
pass
with open(paths["native_regular"], "w", encoding="ascii"):
pass
with open(paths["merge_notdir"], "w", encoding="ascii"):
pass
with open(paths["native_notdir"], "w", encoding="ascii"):
pass
os.symlink("readlink-semantics-loop", paths["merge_loop"])
os.symlink("readlink-semantics-loop", paths["native_loop"])
os.makedirs(paths["merge_private_dir"], exist_ok=True)
os.makedirs(paths["native_private_dir"], exist_ok=True)
os.symlink(target, paths["merge_private_link"])
os.symlink(target, paths["native_private_link"])
try:
cases = []
for bufsiz in (0, 1, 2, 5, 8, len(target), len(target) + 1):
cases.append((
f"success/truncation bufsiz={bufsiz}",
paths["merge_link"],
paths["native_link"],
bufsiz,
errno.EINVAL if bufsiz == 0 else None,
))
cases.extend([
(
"EINVAL non-symlink",
paths["merge_regular"],
paths["native_regular"],
128,
errno.EINVAL,
),
(
"ENOENT missing path",
os.path.join(mount, "readlink-semantics-missing"),
os.path.join(native_dir, "readlink-semantics-missing"),
128,
errno.ENOENT,
),
(
"ENOTDIR non-directory prefix",
os.path.join(paths["merge_notdir"], "child"),
os.path.join(paths["native_notdir"], "child"),
128,
errno.ENOTDIR,
),
(
"ELOOP prefix symlink loop",
os.path.join(paths["merge_loop"], "child"),
os.path.join(paths["native_loop"], "child"),
128,
errno.ELOOP,
),
(
"ENAMETOOLONG long pathname",
os.path.join(mount, "a" * 8192),
os.path.join(native_dir, "a" * 8192),
128,
errno.ENAMETOOLONG,
),
])
os.chmod(paths["merge_private_dir"], 0o600)
os.chmod(paths["native_private_dir"], 0o600)
cases.append((
"EACCES unreadable path prefix",
paths["merge_private_link"],
paths["native_private_link"],
128,
errno.EACCES if os.geteuid() != 0 else None,
))
for case in cases:
err = compare_case(*case)
if err is not None:
print(err, end="")
return 1
# Explicitly guard the prior regression.
rv, err, _ = readlink_raw(paths["merge_link"], 1)
if rv != 1 or err != 0:
print(f"bufsiz=1 expected rv=1 errno=0, got rv={rv} errno={err}", end="")
return 1
return 0
finally:
try:
os.chmod(paths["merge_private_dir"], 0o700)
except (FileNotFoundError, PermissionError):
pass
try:
os.chmod(paths["native_private_dir"], 0o700)
except (FileNotFoundError, PermissionError):
pass
for p in (
paths["merge_private_link"],
paths["native_private_link"],
paths["merge_link"],
paths["native_link"],
paths["merge_regular"],
paths["native_regular"],
paths["merge_notdir"],
paths["native_notdir"],
paths["merge_loop"],
paths["native_loop"],
):
try:
os.unlink(p)
except FileNotFoundError:
pass
for p in (paths["merge_private_dir"], paths["native_private_dir"]):
try:
os.rmdir(p)
except FileNotFoundError:
pass
except OSError:
pass
if __name__ == "__main__":
raise SystemExit(main())
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