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syscall: explain untrusted symlink refusal #1074

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Merged
steadytao merged 2 commits into from
Sep 3, 2026
Merged

syscall: explain untrusted symlink refusal #1074

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69ebbe8
syscall: explain untrusted symlink refusal
steadytao Sep 2, 2026
ef2010a
syscall: emphasise insecure-links warning
steadytao Sep 2, 2026
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4 changes: 4 additions & 0 deletions syscall.c
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Original file line number Diff line number Diff line change
Expand Up @@ -429,6 +429,10 @@ static int ona_open(const char *path, int flags, mode_t mode, char *out_abs, siz
&& ((strcmp(abspath, "/proc") == 0 && strcmp(comp, "self") == 0)
|| (strcmp(abspath, "/dev") == 0 && strcmp(comp, "fd") == 0));
if (!namespace_pin && lst.st_uid != 0 && lst.st_uid != trusted_uid) {
rprintf(FERROR,
"refusing to follow a symlink owned by an untrusted user; "
"use --insecure-links locally or \"insecure links = yes\" in a "
"daemon module ONLY if every path component is trusted\n");
saved_errno = ELOOP;
goto out;
}
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16 changes: 14 additions & 2 deletions testsuite/symlink-race-dest_test.py
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Original file line number Diff line number Diff line change
Expand Up @@ -50,8 +50,20 @@
os.symlink(outside, dest / 'sub') # attacker-owned dest component
os.lchown(dest / 'sub', ATT_UID, ATT_UID)

subprocess.run(rsync_argv('-a', f'{src}/sub/', f'{dest}/sub/'),
stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
proc = subprocess.run(
rsync_argv('-a', f'{src}/sub/', f'{dest}/sub/'),
stdout=subprocess.DEVNULL,
stderr=subprocess.PIPE,
text=True,
)

if proc.returncode == 0:
test_fail("attacker-owned destination symlink was not rejected")
if "refusing to follow a symlink owned by an untrusted user" not in proc.stderr:
test_fail(
"untrusted destination symlink failure omitted the actionable "
f"diagnostic: {proc.stderr!r}"
)

escaped = sorted(p.name for p in outside.iterdir())
if escaped:
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