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userdel: fix user busy detection for threads #1623

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userdel: fix user busy detection for threads #1623

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43a759d
userdel: fix user busy detection for threads
haxtibal May 6, 2026
f013f63
lib: simplify check_status and different_namespace interface
haxtibal May 6, 2026
38ec415
autogen.sh: turn format issues into compiler errors
haxtibal May 7, 2026
3d1b219
lib: apply linux specific pid_t format consistently
haxtibal May 7, 2026
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2 changes: 2 additions & 0 deletions autogen.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -4,8 +4,10 @@ autoreconf -v -f --install "$(dirname "$0")" || exit 1

CFLAGS="-O2"
CFLAGS="$CFLAGS -Wall"
CFLAGS="$CFLAGS -Wformat=2"
CFLAGS="$CFLAGS -Wextra"
CFLAGS="$CFLAGS -Werror=discarded-qualifiers"
CFLAGS="$CFLAGS -Werror=format"
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CFLAGS="$CFLAGS -Werror=implicit-function-declaration"
CFLAGS="$CFLAGS -Werror=implicit-int"
CFLAGS="$CFLAGS -Werror=incompatible-pointer-types"
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21 changes: 10 additions & 11 deletions lib/user_busy.c
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@


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#ifdef __linux__
static int check_status (const char *name, const char *sname, uid_t uid);
static int check_status (const char *name, uid_t uid, pid_t pid, pid_t tid);
static int user_busy_processes (const char *name, uid_t uid);
#else /* !__linux__ */
static int user_busy_utmp (const char *name);
Expand Down Expand Up @@ -94,13 +94,13 @@ user_busy_utmp(const char *name)
#ifdef __linux__
#ifdef ENABLE_SUBIDS
#define in_parentuid_range(uid) ((uid) >= parentuid && (uid) < parentuid + range)
static int different_namespace (const char *sname)
static int different_namespace (pid_t pid, pid_t tid)
{
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/* 41: /proc/xxxxxxxxxx/task/xxxxxxxxxx/ns/user + \0 */
char path[41];
char buf[512], buf2[512];

stprintf_a(path, "/proc/%s/ns/user", sname);
stprintf_a(path, "/proc/%d/task/%d/ns/user", pid, tid);
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if (readlinknul_a(path, buf) == -1)
return 0;
Expand All @@ -116,14 +116,14 @@ static int different_namespace (const char *sname)
#endif /* ENABLE_SUBIDS */


static int check_status (const char *name, const char *sname, uid_t uid)
static int check_status (const char *name, uid_t uid, pid_t pid, pid_t tid)
{
/* 40: /proc/xxxxxxxxxx/task/xxxxxxxxxx/status + \0 */
char status[40];
char line[1024];
FILE *sfile;

stprintf_a(status, "/proc/%s/status", sname);
stprintf_a(status, "/proc/%d/task/%d/status", pid, tid);

sfile = fopen (status, "r");
if (NULL == sfile) {
Expand All @@ -144,7 +144,7 @@ static int check_status (const char *name, const char *sname, uid_t uid)
return 1;
}
#ifdef ENABLE_SUBIDS
if ( different_namespace (sname)
if ( different_namespace (pid, tid)
&& ( have_sub_uids(name, ruid, 1)
|| have_sub_uids(name, euid, 1)
|| have_sub_uids(name, suid, 1))
Expand Down Expand Up @@ -216,7 +216,7 @@ static int user_busy_processes (const char *name, uid_t uid)
}

/* Check if the process is in our chroot */
stprintf_a(root_path, "/proc/%lu/root", (unsigned long) pid);
stprintf_a(root_path, "/proc/%d/root", pid);
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@alejandro-colomar alejandro-colomar May 7, 2026

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For commit 4 ("lib: apply linux specific pid_t format consistently"):

Reviewed-by: Alejandro Colomar <alx@kernel.org>

Thanks!

if (stat (root_path, &sbroot_process) != 0) {
continue;
}
Expand All @@ -225,7 +225,7 @@ static int user_busy_processes (const char *name, uid_t uid)
continue;
}

if (check_status (name, tmp_d_name, uid) != 0) {
if (check_status (name, uid, pid, pid) != 0) {
(void) closedir (proc);
#ifdef ENABLE_SUBIDS
sub_uid_close(true);
Expand All @@ -236,7 +236,7 @@ static int user_busy_processes (const char *name, uid_t uid)
return 1;
}

stprintf_a(task_path, "/proc/%lu/task", (unsigned long) pid);
stprintf_a(task_path, "/proc/%d/task", pid);
task_dir = opendir (task_path);
if (task_dir != NULL) {
while (NULL != (ent = readdir(task_dir))) {
Expand All @@ -247,7 +247,7 @@ static int user_busy_processes (const char *name, uid_t uid)
if (tid == pid) {
continue;
}
if (check_status (name, task_path+6, uid) != 0) {
if (check_status (name, uid, pid, tid) != 0) {
(void) closedir (proc);
(void) closedir (task_dir);
#ifdef ENABLE_SUBIDS
Expand All @@ -272,4 +272,3 @@ static int user_busy_processes (const char *name, uid_t uid)
return 0;
}
#endif /* __linux__ */

1 change: 1 addition & 0 deletions tests/unit/Makefile.am
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Expand Up @@ -100,6 +100,7 @@ test_snprintf_SOURCES = \
$(NULL)
test_snprintf_CFLAGS = \
$(AM_CFLAGS) \
-Wno-format-zero-length \
$(NULL)
test_snprintf_LDFLAGS = \
$(NULL)
Expand Down