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util_lib/elf_info: harden parsing of printk buffer 

Resolves: bz2069200
Upstream: git.kernel.org/pub/scm/utils/kernel/kexec/kexec-tools.git
Conflicts: None

commit f4c59879b830c7d574a953e6ce970ddaf20910d7
Author: Philipp Rudo <prudo@redhat.com>
Date:   Wed Mar 23 16:35:36 2022 +0100

    util_lib/elf_info: harden parsing of printk buffer

    The old printk mechanism (> v3.5.0 and < v5.10.0) had a fixed size
    buffer (log_buf) that contains all messages. The location for the next
    message is stored in log_next_idx. In case the log_buf runs full
    log_next_idx wraps around and starts overwriting old messages at the
    beginning of the buffer. The wraparound is denoted by a message with
    msg->len == 0.

    Following the behavior described above blindly is dangerous as e.g. a
    memory corruption could overwrite (parts of) the log_buf. If the
    corruption adds a message with msg->len == 0 this leads to an endless
    loop when dumping the dmesg. Fix this by verifying that not wrapped
    around before when it encounters a message with msg->len == 0.

    While at it also verify that the index is within the log_buf and thus
    guard against corruptions with msg->len != 0.

    The same bug has been reported and fixed in makedumpfile [1].

    [1] http://lists.infradead.org/pipermail/kexec/2022-March/024272.html

    Signed-off-by: Philipp Rudo <prudo@redhat.com>
    Signed-off-by: Simon Horman <horms@verge.net.au>

Signed-off-by: Philipp Rudo <prudo@redhat.com>
This commit is contained in:
Philipp Rudo 2022-03-28 18:18:13 +02:00
parent 7620d676de
commit 574a202f62
2 changed files with 88 additions and 0 deletions
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86
kexec-tools-2.0.23-05-util_lib_elf_info_harden_parsing_of_printk_buffer.patch Normal file
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@ -0,0 +1,86 @@
commit f4c59879b830c7d574a953e6ce970ddaf20910d7
Author: Philipp Rudo <prudo@redhat.com>
Date: Wed Mar 23 16:35:36 2022 +0100
util_lib/elf_info: harden parsing of printk buffer
The old printk mechanism (> v3.5.0 and < v5.10.0) had a fixed size
buffer (log_buf) that contains all messages. The location for the next
message is stored in log_next_idx. In case the log_buf runs full
log_next_idx wraps around and starts overwriting old messages at the
beginning of the buffer. The wraparound is denoted by a message with
msg->len == 0.
Following the behavior described above blindly is dangerous as e.g. a
memory corruption could overwrite (parts of) the log_buf. If the
corruption adds a message with msg->len == 0 this leads to an endless
loop when dumping the dmesg. Fix this by verifying that not wrapped
around before when it encounters a message with msg->len == 0.
While at it also verify that the index is within the log_buf and thus
guard against corruptions with msg->len != 0.
The same bug has been reported and fixed in makedumpfile [1].
[1] http://lists.infradead.org/pipermail/kexec/2022-March/024272.html
Signed-off-by: Philipp Rudo <prudo@redhat.com>
Signed-off-by: Simon Horman <horms@verge.net.au>
diff --git a/util_lib/elf_info.c b/util_lib/elf_info.c
index d252eff5bd582837595a22aa387f53675c402121..ce71c6055c3a6ce8698d35960a8448be1dc8adc1 100644
--- a/util_lib/elf_info.c
+++ b/util_lib/elf_info.c
@@ -763,8 +763,9 @@ static void dump_dmesg_structured(int fd, void (*handler)(char*, unsigned int))
{
#define OUT_BUF_SIZE 4096
uint64_t log_buf, log_buf_offset, ts_nsec;
- uint32_t log_first_idx, log_next_idx, current_idx, len = 0, i;
+ uint32_t log_buf_len, log_first_idx, log_next_idx, current_idx, len = 0, i;
char *buf, out_buf[OUT_BUF_SIZE];
+ bool has_wrapped_around = false;
ssize_t ret;
char *msg;
uint16_t text_len;
@@ -811,6 +812,7 @@ static void dump_dmesg_structured(int fd, void (*handler)(char*, unsigned int))
}
log_buf = read_file_pointer(fd, vaddr_to_offset(log_buf_vaddr));
+ log_buf_len = read_file_s32(fd, vaddr_to_offset(log_buf_len_vaddr));
log_first_idx = read_file_u32(fd, vaddr_to_offset(log_first_idx_vaddr));
log_next_idx = read_file_u32(fd, vaddr_to_offset(log_next_idx_vaddr));
@@ -882,11 +884,31 @@ static void dump_dmesg_structured(int fd, void (*handler)(char*, unsigned int))
* and read the message at the start of the buffer.
*/
loglen = struct_val_u16(buf, log_offset_len);
- if (!loglen)
+ if (!loglen) {
+ if (has_wrapped_around) {
+ if (len && handler)
+ handler(out_buf, len);
+ fprintf(stderr, "Cycle when parsing dmesg detected.\n");
+ fprintf(stderr, "The prink log_buf is most likely corrupted.\n");
+ fprintf(stderr, "log_buf = 0x%lx, idx = 0x%x\n",
+ log_buf, current_idx);
+ exit(68);
+ }
current_idx = 0;
- else
+ has_wrapped_around = true;
+ } else {
/* Move to next record */
current_idx += loglen;
+ if(current_idx > log_buf_len - log_sz) {
+ if (len && handler)
+ handler(out_buf, len);
+ fprintf(stderr, "Index outside log_buf detected.\n");
+ fprintf(stderr, "The prink log_buf is most likely corrupted.\n");
+ fprintf(stderr, "log_buf = 0x%lx, idx = 0x%x\n",
+ log_buf, current_idx);
+ exit(69);
+ }
+ }
}
free(buf);
if (len && handler)

2
kexec-tools.spec
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@ -117,6 +117,7 @@ Patch603: ./kexec-tools-2.0.23-01-_PATCH_v2_1_3_add_generic_cycle_detection.patc
Patch604: ./kexec-tools-2.0.23-02-_PATCH_v2_2_3_use_pointer_arithmetics_for_dump_dmesg.patch
Patch605: ./kexec-tools-2.0.23-03-_PATCH_v2_3_3_use_cycle_detection_when_parsing_the_prink_log_buf.patch
Patch606: ./kexec-tools-2.0.23-04-_PATCH_print_error_when_reading_with_unsupported_compression.patch
Patch607: ./kexec-tools-2.0.23-05-util_lib_elf_info_harden_parsing_of_printk_buffer.patch
%description
kexec-tools provides /sbin/kexec binary that facilitates a new
@ -138,6 +139,7 @@ tar -z -x -v -f %{SOURCE19}
%patch604 -p1
%patch605 -p1
%patch606 -p1
%patch607 -p1
%ifarch ppc
%define archdef ARCH=ppc