Covered in Documentation/driver-api/early-userspace/buffer-format.rst , initramfs archives can carry an optional "TRAILER!!!" entry which serves as a boundary for collecting and associating hardlinks with matching inode and major / minor device numbers.
Although optional, if hardlinks are found in an archive without a subsequent "TRAILER!!!" entry then the hardlink state hash table is leaked, e.g. unfixed kernel, with initramfs_test.c hunk applied only: unreferenced object 0xffff9405408cc000 (size 8192): comm "kunit_try_catch", pid 53, jiffies 4294892519 hex dump (first 32 bytes): 01 00 00 00 01 00 00 00 00 00 00 00 ff 81 00 00 ................ 00 00 00 00 00 00 00 00 69 6e 69 74 72 61 6d 66 ........initramf backtrace (crc a9fb0ee0): [<0000000066739faa>] __kmalloc_cache_noprof+0x11d/0x250 [<00000000fc755219>] maybe_link.part.5+0xbc/0x120 [<000000000526a128>] do_name+0xce/0x2f0 [<00000000145c1048>] write_buffer+0x22/0x40 [<000000003f0b4f32>] unpack_to_rootfs+0xf9/0x2a0 [<00000000d6f7e5af>] initramfs_test_hardlink+0xe3/0x3f0 [<0000000014fde8d6>] kunit_try_run_case+0x5f/0x130 [<00000000dc9dafc5>] kunit_generic_run_threadfn_adapter+0x18/0x30 [<000000001076c239>] kthread+0xc8/0x100 [<00000000d939f1c1>] ret_from_fork+0x2b/0x40 [<00000000f848ad1a>] ret_from_fork_asm+0x1a/0x30
Fix this by calling free_hash() after initramfs buffer processing in unpack_to_rootfs(). An extra hardlink_seen global is added as an optimization to avoid walking the 32 entry hash array unnecessarily. The expectation is that a "TRAILER!!!" entry will normally be present, and initramfs hardlinks are uncommon.
There is one user facing side-effect of this fix: hardlinks can currently be associated across built-in and external initramfs archives, *if* the built-in initramfs archive lacks a "TRAILER!!!" terminator. I'd consider this cross-archive association broken, but perhaps it's used.
Signed-off-by: David Disseldorp ddiss@suse.de --- init/initramfs.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/init/initramfs.c b/init/initramfs.c index b9cacdc54eaf1..e0b11f8d6f3d6 100644 --- a/init/initramfs.c +++ b/init/initramfs.c @@ -76,6 +76,7 @@ static __initdata struct hash { struct hash *next; char name[N_ALIGN(PATH_MAX)]; } *head[32]; +static __initdata bool hardlink_seen;
static inline int hash(int major, int minor, int ino) { @@ -109,19 +110,21 @@ static char __init *find_link(int major, int minor, int ino, strcpy(q->name, name); q->next = NULL; *p = q; + hardlink_seen = true; return NULL; }
static void __init free_hash(void) { struct hash **p, *q; - for (p = head; p < head + 32; p++) { + for (p = head; hardlink_seen && p < head + 32; p++) { while (*p) { q = *p; *p = q->next; kfree(q); } } + hardlink_seen = false; }
#ifdef CONFIG_INITRAMFS_PRESERVE_MTIME @@ -564,6 +567,8 @@ char * __init unpack_to_rootfs(char *buf, unsigned long len) len -= my_inptr; } dir_utime(); + /* free any hardlink state collected without optional TRAILER!!! */ + free_hash(); kfree(bufs); return message; }