Fix GH-16998: UBSAN warning in rfc1867 #17000
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The "else branch" of `next_line` can reset the `buf_begin` field to NULL, causing the next invocation to pass NULL to `memchr` with a 0 length. When UBSAN is enabled this causes an UBSAN abort. Real world impact is likely none because of the 0 length. To fix this, don't set the pointer to NULL, which means that the `memchr` will return NULL and since `self->bytes_in_buffer < self->bufsize` we return NULL and request more data through `fill_buffer`. That function will reset `buf_begin` and `bytes_in_buffer` so that the next invocation works fine. I chose this solution so we have an invariant that `buf_begin` is never NULL, which makes reasoning easier. An alternative solution is keeping the NULLing of `buf_begin` and add an extra check at the top of `next_line`, but I didn't like special casing this.
arnaud-lb
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Nov 30, 2024
charmitro
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Mar 13, 2025
The "else branch" of `next_line` can reset the `buf_begin` field to NULL, causing the next invocation to pass NULL to `memchr` with a 0 length. When UBSAN is enabled this causes an UBSAN abort. Real world impact is likely none because of the 0 length. To fix this, don't set the pointer to NULL, which means that the `memchr` will return NULL and since `self->bytes_in_buffer < self->bufsize` we return NULL and request more data through `fill_buffer`. That function will reset `buf_begin` and `bytes_in_buffer` so that the next invocation works fine. I chose this solution so we have an invariant that `buf_begin` is never NULL, which makes reasoning easier. An alternative solution is keeping the NULLing of `buf_begin` and add an extra check at the top of `next_line`, but I didn't like special casing this. Closes phpGH-17000.
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The "else branch" of
next_linecan reset thebuf_beginfield to NULL, causing the next invocation to pass NULL tomemchrwith a 0 length. When UBSAN is enabled this causes an UBSAN abort. Real world impact is likely none because of the 0 length.To fix this, don't set the pointer to NULL, which means that the
memchrwill return NULL and sinceself->bytes_in_buffer < self->bufsizewe return NULL and request more data throughfill_buffer. That function will resetbuf_beginandbytes_in_bufferso that the next invocation works fine.I chose this solution so we have an invariant that
buf_beginis never NULL, which makes reasoning easier. An alternative solution is keeping the NULLing ofbuf_beginand add an extra check at the top ofnext_line, but I didn't like special casing this.