`demangle_const` causes infinite recursion and stack overflow

[2019]

Original Post: `https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105115`

The bug is similar to CVE-2021-3530, which was reported here: `https://bugs.launchpad.net/ubuntu/+source/binutils/+bug/1925348`.

Commit: `e84412c6a3c3eed1a4eca5fe18f329bfa7efea40` at `https://github.com/bminor/binutils-gdb`.

The simplified PoC:

$ echo _RYAbB2_ | ./binutils/cxxfilt
Segmentation fault

Root Cause Analysis:

1. In `rust_demangle_callback`, "_R" at beginning causes `rdm.version == 0`[1][2], so `demangle_path` in the else-branch is called[3] with `rdm.sym == "YAbB2_"`, with `rdm.next` field initialized to 0.

2. Next char 'Y' causes `demangle_type` to be called[4] in a switch-case branch, with `rdm.next == 1`.

3. Next char 'A' causes `demangle_type` to be called first[5] to consume char 'b', then `demangle_const` is called[6] with `rdm.next == 3`.

4. Next char 'B' is consumed[7], and "2_" is parsed as `integer_62`[8] to be value 3, and this vlaue is assigned to `rdm.next`, then `demangle_const` is called recursively[9]. However, currently the situation is `rdm.next == 3` again, which is exactly same as last call to `demangle_const`, and this causes infinite recursion.

[1] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1356
[2] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1362
[3] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1453
[4] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L759
[5] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L934
[6] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L938
[7] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1151
[8] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1153
[9] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1158

Possible Fix:

The infinite recursion check added in this [commit](https://github.com/bminor/binutils-gdb/commit/f10f8617a302f45dae721eae0cd659911f03d864) should also be applied to `demangle_const`

[2019 (r3tr0spect2019)]

Created attachment 52721
output.txt is output of ASAN, and inf-recursion is the poc

At commit `b8e92c571baed4e794bd62b7bf417fa8bbaf5c95` of `binutils-gdb`, the given poc can produces crash on `cxxfilt`:

build2/binutils/cxxfilt < inf-recursion

[2019 (r3tr0spect2019)]

Hello, It's already more than one month since my post, and the bug still exists at latest commit (e.i. e84412c6a3c3eed1a4eca5fe18f329bfa7efea40), so I would like to know why it is still `UNCONFIRMED`.

Thanks.

[2019 (r3tr0spect2019)]

The simplified PoC:

$ echo _RYAbB2_ | ./binutils/cxxfilt
Segmentation fault

Root Cause Analysis:

1. In `rust_demangle_callback`, "_R" at beginning causes `rdm.version == 0`[1][2], so `demangle_path` in the else-branch is called[3] with `rdm.sym == "YAbB2_"`, with `rdm.next` field initialized to 0.

2. Next char 'Y' causes `demangle_type` to be called[4] in a switch-case branch, with `rdm.next == 1`.

3. Next char 'A' causes `demangle_type` to be called first[5] to consume char 'b', then `demangle_const` is called[6] with `rdm.next == 3`.

4. Next char 'B' is consumed[7], and "2_" is parsed as `integer_62`[8] to be value 3, and this vlaue is assigned to `rdm.next`, then `demangle_const` is called recursively[9]. However, currently the situation is `rdm.next == 3` again, which is exactly same as last call to `demangle_const`, and this causes infinite recursion.

[1] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1356
[2] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1362
[3] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1453
[4] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L759
[5] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L934
[6] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L938
[7] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1151
[8] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1153
[9] https://github.com/bminor/binutils-gdb/blob/626d0e40e55c35a4f143b70def498734e8ed3c2a/libiberty/rust-demangle.c#L1158

Possible Fix:

The infinite recursion check added in this [commit](https://github.com/bminor/binutils-gdb/commit/f10f8617a302f45dae721eae0cd659911f03d864) should also be applied to `demangle_const`

[Marc Deslauriers (mdeslaur)]

Since the upstream bug is public, I am making this bug public also.

[Redi (redi)]

Maybe a dup of PR 104435