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gdbstub: Fix misuse of isxdigit()

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gdb_read_byte() passes its @ch argument to isxdigit().  Undefined
behavior when the value is negative.  Two callers:

* gdb_chr_receive() passes an uint8_t value.  Safe.

* gdb_handlesig() a char value.  Unsafe.  Not a security issue,
  because the characters come from the gdb client, which is trusted.

The obvious fix would be casting @ch to unsigned char.  But note that
gdb_read_byte() already casts @ch to uint8_t in many places.  Uses of
@ch without such a cast:

(1) Compare to a character constant with == or !=

(2) s->linesum += ch

(3) Store ch or ch ^ 0x20 into s->line_buf[]

(4) Check for invalid RLE count:
    ch < ' ' || ch == '#' || ch == '$' || ch > 126

(5) Pass to isxdigit()

(6) Pass to fromhex()

Change the parameter type from int to uint8_t, and drop the now
redundant casts.  Affects the above uses as follows:

(1) No change: the character constants are all non-negative.

(2) Effectively no change: we only ever use s->linesum & 0xff, and
    s->linesum is int.

(3) No change: s->line_buf[] is char[].

(4) No change.

(5) Avoid undefined behavior.

(6) No change: only reached when isxdigit(ch)

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20190514180311.16028-5-armbru@redhat.com>
This commit is contained in:
Markus Armbruster 2019-05-14 20:03:09 +02:00
parent 046aba169b
commit 33c846efa2
1 changed files with 7 additions and 7 deletions
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14
gdbstub.c
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@ -1987,7 +1987,7 @@ void gdb_do_syscall(gdb_syscall_complete_cb cb, const char *fmt, ...)
va_end(va);
}
static void gdb_read_byte(GDBState *s, int ch)
static void gdb_read_byte(GDBState *s, uint8_t ch)
{
uint8_t reply;
@ -2001,7 +2001,7 @@ static void gdb_read_byte(GDBState *s, int ch)
} else if (ch == '+') {
trace_gdbstub_io_got_ack();
} else {
trace_gdbstub_io_got_unexpected((uint8_t)ch);
trace_gdbstub_io_got_unexpected(ch);
}
if (ch == '+' || ch == '$')
@ -2024,7 +2024,7 @@ static void gdb_read_byte(GDBState *s, int ch)
s->line_sum = 0;
s->state = RS_GETLINE;
} else {
trace_gdbstub_err_garbage((uint8_t)ch);
trace_gdbstub_err_garbage(ch);
}
break;
case RS_GETLINE:
@ -2070,11 +2070,11 @@ static void gdb_read_byte(GDBState *s, int ch)
*/
if (ch < ' ' || ch == '#' || ch == '$' || ch > 126) {
/* invalid RLE count encoding */
trace_gdbstub_err_invalid_repeat((uint8_t)ch);
trace_gdbstub_err_invalid_repeat(ch);
s->state = RS_GETLINE;
} else {
/* decode repeat length */
int repeat = (unsigned char)ch - ' ' + 3;
int repeat = ch - ' ' + 3;
if (s->line_buf_index + repeat >= sizeof(s->line_buf) - 1) {
/* that many repeats would overrun the command buffer */
trace_gdbstub_err_overrun();
@ -2096,7 +2096,7 @@ static void gdb_read_byte(GDBState *s, int ch)
case RS_CHKSUM1:
/* get high hex digit of checksum */
if (!isxdigit(ch)) {
trace_gdbstub_err_checksum_invalid((uint8_t)ch);
trace_gdbstub_err_checksum_invalid(ch);
s->state = RS_GETLINE;
break;
}
@ -2107,7 +2107,7 @@ static void gdb_read_byte(GDBState *s, int ch)
case RS_CHKSUM2:
/* get low hex digit of checksum */
if (!isxdigit(ch)) {
trace_gdbstub_err_checksum_invalid((uint8_t)ch);
trace_gdbstub_err_checksum_invalid(ch);
s->state = RS_GETLINE;
break;
}