Crash in strip_html - attempting to modify const strings

[syldrathecat]

Bitlbee's libpurple code treats messages coming in via prplcb_conv_chat_msg as a mutable string, though it should be treated as a const string.

If a purple plugin calls purple_conv_chat_write with a const string, the same pointer ends up passed to prplcb_conv_chat_msg in bitlbee, and through some process eventually passed to strip_html which attempts to modify the string and crashes.

The problematic line in prplcb_conv_char_msg is: imcb_chat_msg(gc, who, (char *) message, 0, mtime);

Please see ​https://github.com/fcwill/fchat-pidgin/issues/112 for an example crash/backtrace.

The crash only happens since commit 48b5fef4, which enabled HTML processing for all protocols.

[dx]

Neat! Thanks for debugging this. Here's a potential fix, please test: ​https://github.com/bitlbee/bitlbee/commit/0e48e549e7693f665b43bcad5e14ef26447bfe5b

[syldrathecat]

Cross-posting, can confirm that this fix eliminates the crash. :)

[dx]

Merged to master