Commit 59f8bcca authored by John Ogness's avatar John Ogness Committed by Petr Mladek
Browse files

printk: avoid and/or handle record truncation 



If a reader provides a buffer that is smaller than the message text,
the @text_len field of @info will have a value larger than the buffer
size. If readers blindly read @text_len bytes of data without
checking the size, they will read beyond their buffer.

Add this check to record_print_text() to properly recognize when such
truncation has occurred.

Add a maximum size argument to the ringbuffer function to extend
records so that records can not be created that are larger than the
buffer size of readers.

When extending records (LOG_CONT), do not extend records beyond
LOG_LINE_MAX since that is the maximum size available in the buffers
used by consoles and syslog.

Fixes: f5f022e5 ("printk: reimplement log_cont using record extension")
Reported-by: default avatarMarek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: default avatarJohn Ogness <john.ogness@linutronix.de>
Reviewed-by: default avatarPetr Mladek <pmladek@suse.com>
Signed-off-by: default avatarPetr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200930090134.8723-2-john.ogness@linutronix.de
parent f35efc78

kernel/printk/printk.c

+8 −1
Original line number Diff line number Diff line
@@ -1349,6 +1349,13 @@ static size_t record_print_text(struct printk_record *r, bool syslog, 
	size_t len = 0;

	char *next;



	/*

	 * If the message was truncated because the buffer was not large

	 * enough, treat the available text as if it were the full text.

	 */

	if (text_len > buf_size)

		text_len = buf_size;



	prefix_len = info_print_prefix(r->info, syslog, time, prefix);



	/*
@@ -1903,7 +1910,7 @@ static size_t log_output(int facility, int level, enum log_flags lflags, 
		struct printk_record r;



		prb_rec_init_wr(&r, text_len);

		if (prb_reserve_in_last(&e, prb, &r, caller_id)) {

		if (prb_reserve_in_last(&e, prb, &r, caller_id, LOG_LINE_MAX)) {

			memcpy(&r.text_buf[r.info->text_len], text, text_len);

			r.info->text_len += text_len;

			if (lflags & LOG_NEWLINE) {

kernel/printk/printk_ringbuffer.c

+10 −2
Original line number Diff line number Diff line
@@ -202,7 +202,8 @@ 
 *	// specify additional 5 bytes text space to extend

 *	prb_rec_init_wr(&r, 5);

 *

 *	if (prb_reserve_in_last(&e, &test_rb, &r, printk_caller_id())) {

 *	// try to extend, but only if it does not exceed 32 bytes

 *	if (prb_reserve_in_last(&e, &test_rb, &r, printk_caller_id()), 32) {

 *		snprintf(&r.text_buf[r.info->text_len],

 *			 r.text_buf_size - r.info->text_len, "hello");

 *
@@ -1309,6 +1310,7 @@ static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring, 
 * @rb:        The ringbuffer to re-reserve and extend data in.

 * @r:         The record structure to allocate buffers for.

 * @caller_id: The caller ID of the caller (reserving writer).

 * @max_size:  Fail if the extended size would be greater than this.

 *

 * This is the public function available to writers to re-reserve and extend

 * data.
@@ -1343,7 +1345,7 @@ static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring, 
 *            @r->info->text_len after concatenating.

 */

bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,

			 struct printk_record *r, u32 caller_id)

			 struct printk_record *r, u32 caller_id, unsigned int max_size)

{

	struct prb_desc_ring *desc_ring = &rb->desc_ring;

	struct printk_info *info;
@@ -1389,6 +1391,9 @@ bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer 
		if (!data_check_size(&rb->text_data_ring, r->text_buf_size))

			goto fail;



		if (r->text_buf_size > max_size)

			goto fail;



		r->text_buf = data_alloc(rb, &rb->text_data_ring, r->text_buf_size,

					 &d->text_blk_lpos, id);

	} else {
@@ -1410,6 +1415,9 @@ bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer 
		if (!data_check_size(&rb->text_data_ring, r->text_buf_size))

			goto fail;



		if (r->text_buf_size > max_size)

			goto fail;



		r->text_buf = data_realloc(rb, &rb->text_data_ring, r->text_buf_size,

					   &d->text_blk_lpos, id);

	}

kernel/printk/printk_ringbuffer.h

+1 −1
Original line number Diff line number Diff line
@@ -303,7 +303,7 @@ static inline void prb_rec_init_wr(struct printk_record *r, 
bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,

		 struct printk_record *r);

bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb,

			 struct printk_record *r, u32 caller_id);

			 struct printk_record *r, u32 caller_id, unsigned int max_size);

void prb_commit(struct prb_reserved_entry *e);

void prb_final_commit(struct prb_reserved_entry *e);

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