pstore: pass allocated memory region back to caller

The buf_lock cannot be held while populating the inodes, so make the backend
pass forward an allocated and filled buffer instead. This solves the following
backtrace. The effect is that "buf" is only ever used to notify the backends
that something was written to it, and shouldn't be used in the read path.

To replace the buf_lock during the read path, isolate the open/read/close
loop with a separate mutex to maintain serialized access to the backend.

Note that is is up to the pstore backend to cope if the (*write)() path is
called in the middle of the read path.

[   59.691019] BUG: sleeping function called from invalid context at .../mm/slub.c:847
[   59.691019] in_atomic(): 0, irqs_disabled(): 1, pid: 1819, name: mount
[   59.691019] Pid: 1819, comm: mount Not tainted 3.0.8 #1
[   59.691019] Call Trace:
[   59.691019]  [<810252d5>] __might_sleep+0xc3/0xca
[   59.691019]  [<810a26e6>] kmem_cache_alloc+0x32/0xf3
[   59.691019]  [<810b53ac>] ? __d_lookup_rcu+0x6f/0xf4
[   59.691019]  [<810b68b1>] alloc_inode+0x2a/0x64
[   59.691019]  [<810b6903>] new_inode+0x18/0x43
[   59.691019]  [<81142447>] pstore_get_inode.isra.1+0x11/0x98
[   59.691019]  [<81142623>] pstore_mkfile+0xae/0x26f
[   59.691019]  [<810a2a66>] ? kmem_cache_free+0x19/0xb1
[   59.691019]  [<8116c821>] ? ida_get_new_above+0x140/0x158
[   59.691019]  [<811708ea>] ? __init_rwsem+0x1e/0x2c
[   59.691019]  [<810b67e8>] ? inode_init_always+0x111/0x1b0
[   59.691019]  [<8102127e>] ? should_resched+0xd/0x27
[   59.691019]  [<8137977f>] ? _cond_resched+0xd/0x21
[   59.691019]  [<81142abf>] pstore_get_records+0x52/0xa7
[   59.691019]  [<8114254b>] pstore_fill_super+0x7d/0x91
[   59.691019]  [<810a7ff5>] mount_single+0x46/0x82
[   59.691019]  [<8114231a>] pstore_mount+0x15/0x17
[   59.691019]  [<811424ce>] ? pstore_get_inode.isra.1+0x98/0x98
[   59.691019]  [<810a8199>] mount_fs+0x5a/0x12d
[   59.691019]  [<810b9174>] ? alloc_vfsmnt+0xa4/0x14a
[   59.691019]  [<810b9474>] vfs_kern_mount+0x4f/0x7d
[   59.691019]  [<810b9d7e>] do_kern_mount+0x34/0xb2
[   59.691019]  [<810bb15f>] do_mount+0x5fc/0x64a
[   59.691019]  [<810912fb>] ? strndup_user+0x2e/0x3f
[   59.691019]  [<810bb3cb>] sys_mount+0x66/0x99
[   59.691019]  [<8137b537>] sysenter_do_call+0x12/0x26
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>

drivers/acpi/apei/erst.c

@@ -932,7 +932,8 @@ static int erst_check_table(struct acpi_table_erst *erst_tab)
 static int erst_open_pstore(struct pstore_info *psi);
 static int erst_close_pstore(struct pstore_info *psi);
 static ssize_t erst_reader(u64 *id, enum pstore_type_id *type,
-			   struct timespec *time, struct pstore_info *psi);
+			   struct timespec *time, char **buf,
+			   struct pstore_info *psi);
 static int erst_writer(enum pstore_type_id type, u64 *id, unsigned int part,
 		       size_t size, struct pstore_info *psi);
 static int erst_clearer(enum pstore_type_id type, u64 id,
@@ -986,17 +987,23 @@ static int erst_close_pstore(struct pstore_info *psi)
 }
 
 static ssize_t erst_reader(u64 *id, enum pstore_type_id *type,
-			   struct timespec *time, struct pstore_info *psi)
+			   struct timespec *time, char **buf,
+			   struct pstore_info *psi)
 {
 	int rc;
 	ssize_t len = 0;
 	u64 record_id;
-	struct cper_pstore_record *rcd = (struct cper_pstore_record *)
-					(erst_info.buf - sizeof(*rcd));
+	struct cper_pstore_record *rcd;
+	size_t rcd_len = sizeof(*rcd) + erst_info.bufsize;
 
 	if (erst_disable)
 		return -ENODEV;
 
+	rcd = kmalloc(rcd_len, GFP_KERNEL);
+	if (!rcd) {
+		rc = -ENOMEM;
+		goto out;
+	}
 skip:
 	rc = erst_get_record_id_next(&reader_pos, &record_id);
 	if (rc)
@@ -1004,22 +1011,27 @@ static ssize_t erst_reader(u64 *id, enum pstore_type_id *type,
 
 	/* no more record */
 	if (record_id == APEI_ERST_INVALID_RECORD_ID) {
-		rc = -1;
+		rc = -EINVAL;
 		goto out;
 	}
 
-	len = erst_read(record_id, &rcd->hdr, sizeof(*rcd) +
-			erst_info.bufsize);
+	len = erst_read(record_id, &rcd->hdr, rcd_len);
 	/* The record may be cleared by others, try read next record */
 	if (len == -ENOENT)
 		goto skip;
-	else if (len < 0) {
-		rc = -1;
+	else if (len < sizeof(*rcd)) {
+		rc = -EIO;
 		goto out;
 	}
 	if (uuid_le_cmp(rcd->hdr.creator_id, CPER_CREATOR_PSTORE) != 0)
 		goto skip;
 
+	*buf = kmalloc(len, GFP_KERNEL);
+	if (*buf == NULL) {
+		rc = -ENOMEM;
+		goto out;
+	}
+	memcpy(*buf, rcd->data, len - sizeof(*rcd));
 	*id = record_id;
 	if (uuid_le_cmp(rcd->sec_hdr.section_type,
 			CPER_SECTION_TYPE_DMESG) == 0)
@@ -1037,6 +1049,7 @@ static ssize_t erst_reader(u64 *id, enum pstore_type_id *type,
 	time->tv_nsec = 0;
 
 out:
+	kfree(rcd);
 	return (rc < 0) ? rc : (len - sizeof(*rcd));
 }
 

drivers/firmware/efivars.c

@@ -457,7 +457,8 @@ static int efi_pstore_close(struct pstore_info *psi)
 }
 
 static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
-			       struct timespec *timespec, struct pstore_info *psi)
+			       struct timespec *timespec,
+			       char **buf, struct pstore_info *psi)
 {
 	efi_guid_t vendor = LINUX_EFI_CRASH_GUID;
 	struct efivars *efivars = psi->data;
@@ -478,7 +479,11 @@ static ssize_t efi_pstore_read(u64 *id, enum pstore_type_id *type,
 				timespec->tv_nsec = 0;
 				get_var_data_locked(efivars, &efivars->walk_entry->var);
 				size = efivars->walk_entry->var.DataSize;
-				memcpy(psi->buf, efivars->walk_entry->var.Data, size);
+				*buf = kmalloc(size, GFP_KERNEL);
+				if (*buf == NULL)
+					return -ENOMEM;
+				memcpy(*buf, efivars->walk_entry->var.Data,
+				       size);
 				efivars->walk_entry = list_entry(efivars->walk_entry->list.next,
 					           struct efivar_entry, list);
 				return size;

fs/pstore/platform.c

@@ -167,6 +167,7 @@ int pstore_register(struct pstore_info *psi)
 	}
 
 	psinfo = psi;
+	mutex_init(&psinfo->read_mutex);
 	spin_unlock(&pstore_lock);
 
 	if (owner && !try_module_get(owner)) {
@@ -195,30 +196,32 @@ EXPORT_SYMBOL_GPL(pstore_register);
 void pstore_get_records(int quiet)
 {
 	struct pstore_info *psi = psinfo;
+	char			*buf = NULL;
 	ssize_t			size;
 	u64			id;
 	enum pstore_type_id	type;
 	struct timespec		time;
 	int			failed = 0, rc;
-	unsigned long		flags;
 
 	if (!psi)
 		return;
 
-	spin_lock_irqsave(&psinfo->buf_lock, flags);
+	mutex_lock(&psi->read_mutex);
 	rc = psi->open(psi);
 	if (rc)
 		goto out;
 
-	while ((size = psi->read(&id, &type, &time, psi)) > 0) {
-		rc = pstore_mkfile(type, psi->name, id, psi->buf, (size_t)size,
+	while ((size = psi->read(&id, &type, &time, &buf, psi)) > 0) {
+		rc = pstore_mkfile(type, psi->name, id, buf, (size_t)size,
 				  time, psi);
+		kfree(buf);
+		buf = NULL;
 		if (rc && (rc != -EEXIST || !quiet))
 			failed++;
 	}
 	psi->close(psi);
 out:
-	spin_unlock_irqrestore(&psinfo->buf_lock, flags);
+	mutex_unlock(&psi->read_mutex);
 
 	if (failed)
 		printk(KERN_WARNING "pstore: failed to load %d record(s) from '%s'\n",

include/linux/pstore.h

@@ -35,10 +35,12 @@ struct pstore_info {
 	spinlock_t	buf_lock;	/* serialize access to 'buf' */
 	char		*buf;
 	size_t		bufsize;
+	struct mutex	read_mutex;	/* serialize open/read/close */
 	int		(*open)(struct pstore_info *psi);
 	int		(*close)(struct pstore_info *psi);
 	ssize_t		(*read)(u64 *id, enum pstore_type_id *type,
-			struct timespec *time, struct pstore_info *psi);
+			struct timespec *time, char **buf,
+			struct pstore_info *psi);
 	int		(*write)(enum pstore_type_id type, u64 *id,
 			unsigned int part, size_t size, struct pstore_info *psi);
 	int		(*erase)(enum pstore_type_id type, u64 id,