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python re bug #81508

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aixianle mannequin opened this issue Jun 18, 2019 · 5 comments
Closed

python re bug #81508

aixianle mannequin opened this issue Jun 18, 2019 · 5 comments
Labels
3.7 (EOL) end of life topic-regex type-crash A hard crash of the interpreter, possibly with a core dump

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@aixianle
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Mannequin

aixianle mannequin commented Jun 18, 2019

BPO 37327
Nosy @ezio-melotti, @aldwinaldwin

Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.

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GitHub fields:

assignee = None
closed_at = <Date 2019-06-18.10:19:49.677>
created_at = <Date 2019-06-18.06:17:11.564>
labels = ['expert-regex', '3.7', 'invalid', 'type-crash']
title = 'python re bug'
updated_at = <Date 2019-06-18.10:19:49.674>
user = 'https://bugs.python.org/aixianle'

bugs.python.org fields:

activity = <Date 2019-06-18.10:19:49.674>
actor = 'mrabarnett'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-18.10:19:49.677>
closer = 'mrabarnett'
components = ['Regular Expressions']
creation = <Date 2019-06-18.06:17:11.564>
creator = 'aixian le'
dependencies = []
files = []
hgrepos = []
issue_num = 37327
keywords = []
message_count = 5.0
messages = ['345953', '345955', '345957', '345958', '345978']
nosy_count = 4.0
nosy_names = ['ezio.melotti', 'mrabarnett', 'aldwinaldwin', 'aixian le']
pr_nums = []
priority = 'normal'
resolution = 'not a bug'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'crash'
url = 'https://bugs.python.org/issue37327'
versions = ['Python 3.6', 'Python 3.7']
@aixianle
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aixianle mannequin commented Jun 18, 2019

the code is:
banner = "HTTP/1.0 404 Not Found\r\nDate: Mon, 17 Jun 2019 13:15:44 GMT\r\nServer: \r\nConnection: close\r\nContent-Type: text/html\r\n\r\n<HTML><HEAD><TITLE>404 Not Found</TITLE></HEAD>\r\n<BODY><H1>404 Not Found</H1>\r\nThe requested URL /PSIA/index was not found on this server.\r\n</BODY></HTML>\r\n"
regex = "^HTTP/1\\.0 404 Not Found\\r\\n(?:[^\<]+|<(?!/head>))*?<style>"
print("start")
regex_re = re.compile(regex)
print("start1")
regex_re.search(banner)
print("end")
when I execute this code ,python cannot finished.

@aixianle aixianle mannequin added topic-regex type-crash A hard crash of the interpreter, possibly with a core dump labels Jun 18, 2019
@aixianle
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aixianle mannequin commented Jun 18, 2019

the code is:
banner = "HTTP/1.0 404 Not Found\r\nDate: Mon, 17 Jun 2019 13:15:44 GMT\r\nServer: \r\nConnection: close\r\nContent-Type: text/html\r\n\r\n<HTML><HEAD><TITLE>404 Not Found</TITLE></HEAD>\r\n<BODY><H1>404 Not Found</H1>\r\nThe requested URL /PSIA/index was not found on this server.\r\n</BODY></HTML>\r\n"
regex = "^HTTP/1\\.0 404 Not Found\\r\\n(?:[^\<]+|<(?!/head>))*?<style>"
print("start")
regex_re = re.compile(regex)
print("start1")
regex_re.search(banner)
print("end")
when I execute this code ,python cannot finished.

@aixianle aixianle mannequin added the 3.7 (EOL) end of life label Jun 18, 2019
@aldwinaldwin
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aldwinaldwin mannequin commented Jun 18, 2019

When I run the regex on https://regex101.com/, after some small adjustments ("HTTP\/1\.0" and "\/head"), it mentions 'Catastrophic backtracking has been detected and the execution of your expression has been halted.' I don't know much about regex, but it seems there is some eternal loop or something.

I'd suggest to try to make the regex work first on other regex compiler, before calling it a python bug.

@aldwinaldwin
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aldwinaldwin mannequin commented Jun 18, 2019

neither the banner contains "<style>"

@mrabarnett
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mrabarnett mannequin commented Jun 18, 2019

The problem is the "(?:[^\<]+|<(?!/head>))*?".

If I simplify it a little I get "(?:[^\<]+)*?", which is a repeat within a repeat.

There are many ways in which it could match, and if what follows fails to match (it doesn't because there's no "<style>" in the target string, as Aldwin pointed out), it'll try them all, which can take a long time.

@mrabarnett mrabarnett mannequin closed this as completed Jun 18, 2019
@mrabarnett mrabarnett mannequin added the invalid label Jun 18, 2019
@ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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