[bluez/bluez] 1663ae: Fix heap-buffer-overflow in sdp_xml.c:compute_seq_...

[Oliver Chang <noreply@github.com>]

  Branch: refs/heads/990970
  Home:   https://github.com/bluez/bluez
  Commit: 1663ae444fa2a670d2e7cc2fdfc3eb3e057621e6
      https://github.com/bluez/bluez/commit/1663ae444fa2a670d2e7cc2fdfc3eb3e057621e6
  Author: Oliver Chang <ochang@google.com>
  Date:   2025-08-13 (Wed, 13 Aug 2025)

  Changed paths:
    M src/sdp-xml.c

  Log Message:
  -----------
  Fix heap-buffer-overflow in sdp_xml.c:compute_seq_size

https://issues.oss-fuzz.com/issues/42516062
https://oss-fuzz.com/testcase-detail/5896441415729152

This can be triggered by using an input of
`<sequence><foo/><text/></sequence>` against the harness in
https://github.com/google/oss-fuzz/blob/master/projects/bluez/fuzz_xml.c

The root cause of the heap-buffer-overflow was incorrect stack
management in the SDP XML parser (element_end function) that led to type
confusion.

When an XML element failed to parse (e.g., an unrecognized tag like
<foo/>), its corresponding entry was left on the parser stack because
the we returned early if data was NULL.

With the input <sequence><foo/><text/></sequence>, <foo/> failed parsing
and remained on the stack with a NULL data. Then <text/> was parsed and
also remained on the stack because it's only popped if
ctx_data->stack_head->next->data != NULL.

When </sequence> was encountered, the parser then mistakenly used the
data from <text/> (which was now at the top of the stack) as the
sequence data.  This led to a type confusion: the TEXT data's string
pointer (val.str) was interpreted as a sequence pointer (val.dataseq).
This pointer pointed to a 1-byte allocation (for the empty string). The
code then tried to dereference this pointer as an sdp_data_t struct to
calculate the sequence size, leading to the out-of-bounds read.

To fix this, in element_end, ensure that the stack is popped even if the
element's data failed to parse. This prevents the stack
desynchronization.



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