Certain errors during IMPORT_STAR can leak a reference

[corsix]

BPO	29655
Nosy	@berkerpeksag, @serhiy-storchaka, @Carreau, @corsix
PRs	bpo-29655: Fix import start can leak a reference. #301 [3.6] bpo-29655: Fixed possible reference leaks in import *. (#301) #348 [3.5] bpo-29655: Fixed possible reference leaks in import *. (#301) #349 bpo-29655: Fixed possible reference leaks in import *. (#301) #510
Files	issue29655-2.7.patch

^{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 2017-03-15.10:49:37.372>
created_at = <Date 2017-02-25.21:26:53.534>
labels = ['interpreter-core', 'performance']
title = 'Certain errors during IMPORT_STAR can leak a reference'
updated_at = <Date 2017-03-24.23:45:06.809>
user = 'https://github.com/corsix'

bugs.python.org fields:

activity = <Date 2017-03-24.23:45:06.809>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2017-03-15.10:49:37.372>
closer = 'berker.peksag'
components = ['Interpreter Core']
creation = <Date 2017-02-25.21:26:53.534>
creator = 'Peter Cawley'
dependencies = []
files = ['46678']
hgrepos = []
issue_num = 29655
keywords = ['patch']
message_count = 8.0
messages = ['288582', '288664', '288665', '288694', '290263', '290362', '290363', '290399']
nosy_count = 4.0
nosy_names = ['berker.peksag', 'serhiy.storchaka', 'mbussonn', 'Peter Cawley']
pr_nums = ['301', '348', '349', '510']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'resource usage'
url = 'https://bugs.python.org/issue29655'
versions = ['Python 2.7']

[corsix]

In the implementation of the IMPORT_STAR opcode, if the call to PyFrame_FastToLocalsWithError fails, or f_locals is NULL, then control flow jumps to the error handler without performing a decref on the "from" variable. As the "from" variable is initialised by POPping from the stack, the reference is leaked.

[serhiy-storchaka]

It looks to me that 2.7 has this bug.

[berkerpeksag]

I ignored 2.7 because you know... it's 2.7 :) And you said [1] that it doesn't have a big effect on real applications.

[1] #301 (comment)

[serhiy-storchaka]

But it is *very easy* to fix this bug in 2.7.

[serhiy-storchaka]

New changeset 9fbb65e by Serhiy Storchaka in branch '2.7':
bpo-29655: Fixed possible reference leaks in import *. (#301) (#510)
9fbb65e

[berkerpeksag]

New changeset 0dadf56 by Berker Peksag in branch '3.5':
bpo-29655: Fixed possible reference leaks in import *. (#301) (#349)
0dadf56